UC BERKELEY MASTER NEGATIVE STORAGE NUMBER 03-67.59 (National version of master negative storage number: CU SN03067.59) MICROFILMED 2003 UNIVERSITY OF CALIFORNIA AT BERKELEY LIBRARY PHOTOGRAPHIC SERVICE REPRODUCTION AVAILABLE THROUGH INTERLIBRARY LOAN OFFICE MAIN LIBRARY UNIVERSITY OF CALIFORNIA BERKELEY, CA 94720-6000 COPYRIGHT The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted materials including foreign works under certain conditions. In addition, the United States extends protection to foreign works by means of various international conventions, bilateral agreements, and proclamations. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of “fair use," that user may be liable for copyright infringement. University of California at Berkeley reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. Tinkham, John Howard A digest of "L'architecture du sol de la France" by O. Barre [19157] BIBLIOGRAPHIC RECORD TARGET University of California at Berkeley Library Master negative storage number: 03-67.59 (national version of the master negative storage number: CU SN03067.59) GLADIS NUMBER: 1847892081 AD:991013/FZB LEVEL:D BlL7h:am DCF:a CSC:4d MOD: EL:7 UD:030604 /MAP CP:cau L:eng INT: GPC: B10: Fic: CON: ARCV: PC:s PD:1915/ REP: CP1: FS1: T1C: 1:0 CUscCl SbDISS.TINKHAM.GEOL 1915 1 7Tinkham, John Howard. 12 A digest of "L'architecture du sol de la France” by O. Barre. $c[19157] [iv], 49 p. :8bcol. ill, maps ;$c29 cm. Includes bibliographical references. 20 University of California, Berkeley.$bDept. of Geology and Geophysics$xDissertations. 0 Dissertations, AcademicS$xUCBSxGeologyS$Sy1911-1920. Microfilmed by University of California Library Photographic Service, Berkeley, CA FILMED AND PROCESSED BY LIBRARY PHOTOGRAPHIC SERVICE, UNIVERSITY OF CALIFORNIA, BERKELEY, 94720 DATE: 7/03 REDUCTION: 10 X PM-1 3%:"x4" PHOTOGRAPHIC MICROCOPY TARGET NBS 1010a ANSI/ISO #2 EQUIVALENT 10 Be 2 = M32 = Eu es LL a BE 90 40 . hk Bae t—— . —————— l= et ne ry PEPER T gl agg" ge) - 2A at ®l1 elt alt, tt, ol s” subi ofr ei LOI 8 kl dill Gl hd i] ga - a EO YS I AT TNT I A ; i. ETAT TT ” _— ' TINKHAM Geo L 8 121s ACT A DIGEST OF "L'ARCHITECTURE DU SOL DE LA FRANCE" By O. Barre - J. Howard Tinkham ~ 191% DIGEST of L'ARCHITECTURE DU SOL DE LA FRANCE FOREWORD TABLE OF CONTENTS Page The following pages comprise a brief summary and digest of INTRODUCTION =~ : - - - - - - - - -] "L'Architecture du Sol de la France", a volume by M. O.Barre dealing Materials of the Soil - - - - - - - - - 1 with the physiography and geologic history of France, with some general Architecture or Tectonics of the Earth's Crust =- - - - 3 consideration of Central Europe as a whole. Sculpture of the Earth's Crust - - - - - - - 4 In summarizing in English a work of this nature, the student Geographic Evolution =~ - - - - - - - - b mst necessarily encounter some words, some phrases, unsuited to literal GEOGRAPHIC EVOLUTION OF CENTRAL EUROPE - - - - - 6 translation. For this reason, the French nomenclature has been used in The Primary Era - - - - - - - - - a number of instances where it is believed the meaning is apparent. : Secondary Era =~ - - - - - - - - - 7 M. Barrd's work, completed some twemty years ago, may well Tertiary Era = - - - - - - - - - 8 be compared with the more recent geologic treatises. It is significant Quaternary Era - - - - - - - , - - 8 that the Ordovician period of the Palaeozoic era is not recognized Geographic Consequences - - - - - - - - 9 throughout the book. In only one instance is the Archaeozoic era allud- ed to, and little or no mention is made of the existence of pre=Cambrian CHAPTER ONE - GENERAL RELIEF FORMS OF FRANCE - - - - 9 rocks in the Central European area. The oldest strata are vaguely re- GEOLOGIC HISTORY OF THE AREA OF FRANCE - - - - - 10 ferred to as "les terrain anciems" and "le socle hercynien". Primary Era - = - - - - - - - - 10 The tetrahedral theory, now generally discredited, is cited Secondary Era ~ = - - - - - - - - 10 in explanation of the present distribution of the continental amd geo~ Tertiary Era =~ = - " - re - - - - 11 synclinal (positive and negative) areas of the globe. 3 Quaternary - = - - - ne - - 11 Little stress is placed upon the petrography of the several Geographic Consequences - - - - - - - - 11 regions discussed, though a clear idea is presented of their topographic structure and geographic evolution. The chapters on the Alps amd the CHAPTER TWO - THE REGION TO THE NORTH AND NORTH WEST - - - 18 Pyrenees are of especial interest. Summary of Geologic History - - - - - - - 13 : WESTERN PARISIAN REGION - _ - - - - - - 14 The maps on pages 15a and 19a of this report may be used to General Considerations - » - - - - - - 14 locate most of the major geographic divisions referred to in the text. Details = - - - - - - - - - 15 General Remarks on tue Hydrography - - - - - - 15 THE BELGIAN REGION - - - - - - - - - 15 General Considerations ~ - , - - - - - 15 Details of the Several Districts ~- - - »- - - 16 ®kokk PRIMARY PLATEAUX =~ - - - - - - - - ~- 16 General Considerations - - - - - - - - 16 General Remarks on the Hydrography - - - - - - 17 CHAPTER THREE - REGION TO THE NORTH-EAST - - - - - 17 Geoldgic History; Great Geographic Divisions - - - - 17 . The Rhine Territory - - - - - - - - - 18 The Vosges. The Mountains of Palatinate - - - - - 19 Lorraine =~ - - - - - - - - - 19 HIGH VALLEY OF THE SAONE =~ - - - - - - - 20 EASTERN PARISIAN REGION - - - - - - - - 3] . Topographic Characteristics =~ - - - - - - 21 JHXYER > = = = we we . ww. ms CHAPTER FOUR - REGION TO THE EAST AND SOUTHEAST i TABLE OF CONTENTS (cont'd) shat ' TABLE OF CONTENTS (cont'd) Page CHAPTER FOUR - REGION TO THE EAST AND SOUTHEAST ~- - - - 23 General Considerations - - - - - - - - 23 CHAPTER EIGHT - THE SEA COASTS - - - - - - - - 33 Geologic Evolution ~ - - - - = - - - RA Origin of the Shore Lines - - - - - i: - - 42 MEJURA =~ = - « = = ‘= = = = = B55 SHORE LINES OF THE MEDITERRANEAN - = = = = = = 43 Arcanitectural Distriovution =~ - - - - - - 2b Gulf of Genoa and Gulf of Lion -~ - - - - - - 43 Sculpture of the Ground - - - - - - - - 25 Shore Lines of La Provence - - - “ - - - - 43 General Remarks on tie Eyirograply - mew wie Delta of the Rhone ~- ~ - - me. a Marginal Zones - - - - - - 26 Coasts of the langrease and of ‘ue Roussillon - - - - 44 THE ALPS = - - - - - - - - - - 6 Corsica ~ - - - - - - - - - 44 General Architecture - - - - - - - - &6 THE ATLANTIC SEA COASTS - - - - - . - - - 88 Sculpture of the Ground -» = = = = = = «27 Origin of the Continental Platform - - we ow 4B Glaciation - - - - - - - - - 87 The Gulf of Gascony and the British Chanel - - - - 46 Geographic Pivletee = 2 = x = = 3 2 28 Coasts of 1'Aquitaine » ~~ «= « + +. Ww oo. a9 Savoie = - - - . - - - - - 25 Coasts of l'Armorique ~- - - > - - - - - 47 Sub-Alpine Part - - m - - - - - &8 Coasts of the Parisian Region -~ - - - - - - 48 Alpine Part - - - - - - - - - 28 Dauphiné - - - - - w- - - &8 ERE RH Hydrography of the Deuphind - - - = - = 28 Haute~-Provence: Comte de Nice =~ » - - - = 29 id ——— HAS PEERY » : . i > . = s Pe | TABLE OF MAPS AND ILLUSTRATIONS Plateaux de raccord “ - - - - - - - 30 Mountains of the Sasse-Provemee - ~ = - - = 50 Geosynclines and Continental Areas of the World - - - - 4 Maures and Esterel - - - - - - - - - 80 Positions of the Successive Great Continental Folds of Europe - 6 { VAMEYOR SERINE = = = ww = = = = = 83 ¥ Map of the Buropean Region at the Beginning of the Permian Period - 8 : : Map of Central Europe - - - - - - 10 CHAPTER FIVE - REGION TO THE SOUTH AND SOUTH-WEST - - - 31 Map of Northern France - - - - - - - - - 1B Historical Geologic Summary. Major Divisious ~- - - - 31 Outline Map of France - - - - - - - - 19 THE PYRENEES =~ w = 2m. = = be = 31 Map Showing Drainage amd Structure in the Vicinity of Saris - = 22 General Arcnitecture - cm EW ww - = 3 Present Shore Lines and Hypothetical Shore Lines of France - = 42 Sculpture of tae Grouud = - - - - - - - 32 Geologic Map of Corsica = - - - - - 48, CORBIERES = - - - - - - - - - - 33 | Map Showing Principel Undulations in the Angli-Paricisn Seziva - 49 MONTAGNE NOIRE = - - - - - - - - - 33 BAS-LANGUEDOC = - - - - - - - - - 31 - AQUITAINE ~ - - “ w - - - - - - 34 * CHAPTER SIX - REGION TO THE WEST =~ - - _ - - - 3b Ma jor Divisions - - - - - - - - - 35 MASSIF ARMORICAIN o i n- - - - - - - 3b General Considerations 3b Brittany = - - - - - - - - - 3b Cotentin =~ - « ew wea agg EE Vendée =~ - - - _ n - - - - - 36 MARGINAL REGIONS ee ee gL Hydrography - - - = - - - = - - 37 CHAPTER SEVEN - CENTRAL REGION OF FRANCE ~ - - - - 38 General Considerations - - - ol - - - 38 Major Divisions of the Massif ancien Ke - - - - 40 ( Eastern Escarpment - - - - - - - - - 40 : 5 Western Part of the Massif ancien - - - - - - 41 | Borders of the Massif ancien =~ - - - - - - 41 L'ARCHITECTURE DU SOL DE LA FRANCE ' O. Barre INTRODUCTION The present form of the terrestial globe is in a transitory state. From tne moment the eartn was in the planetary phase, tnatv is from the time the first solid crust had begun to form in a definite fashion, certain geographic features were established. {ince then that distrioution has been constantly changing to evolve the present state. The geographic state at any one determined instant, for example that iu wnica we now find ourselves, is tnerefore a sort of syntnesis of all of a series of distributions which have gone before. It is therefore necessary to study these past forms in order to more fully understand the present. The forces wnicn contribute to tne evolution of the eartn forms are due to two main causes, e.g. (1) the cooling of the eartn and, (2) the solar energy. To the former must be attributed the forms of reliei, to the latter tneir progressive wear. It is, in erfect, tie cooling of the eartn which, devermining its contraction, causes the superricial crust to be folded and fashioned in accordance witn tuat contraction; and it is the solar energy which sustains the organic forces and puts in movement the suriace waters, destructive agents wnose continued action tends to level the suriace of the earti. Moreover the formation and progressive wearing away of reliexr features as a result of many variable forces have modified tne eartn's crust most profoundly since its initial state. 4 study of these progressive changes of nature and their influence upon geographic evolution must be divided into taree distinct factors: lst the nature of the materials of the ground; 2nd their structural (or architectural) arrangement, znd : 3rd their sculpture and progressive wear under the action of exterior agents. The study of the nature of the materials and their struct- ural disposition constitutes the domain of geology. 4s to the sculp- ture of the eartn this becomes the object of a special branch of studies whose principal results have been indicated, in France by MM. de la Noe and de liargerie in their work on "les Formes du terrain". Without pretending to resume in a few lines all that is relative to these sciences we wish to bring to light the essential principles, those with which all must be familiar in the study of geology. MATERIALS OF THE SOIL (GROUND) It is generally admitted that the terrestial globe, which was gaseous at its origin, passed next into the fluid state. The cooling, continuing its progress, formed a crust comparable, without doubt, to the scoria on a metallic mass in fusion. That crust, at first -d instable «nd subject to incessant modifications under the influence of heat, chemical action, and mighty currents developed in the fluid mass, solidified definitely after a long period of cemturies, constituting the first ground (terrain). This terrain, to which has been given the name "Archean terrain", serves as a sort of base or foundation for all the edifice of the terrestial crust. It is composed of diverse elements, but having allied characteristics. The gneiss is the type most common in this group of crystalline rocks. From the moment when that irchean crust had definitely solid- ified the molten rock in the interior was isolated from the exterior gaseous envelope. To that epoch dates the separation between the earth and its atmosphere, the first formation of oceanic provinces, and final- ly without doubt the most ancient manifestations of life. The solidification of this crust followed by the action of many modifying agents - chemical and organic agents, surface waters, the atmosphere, etc. — has formed new rock materials differing completely from the initial Archean crust although derived directly from it. We recognize two new classes of materials: the eruptive materials and the sedimentary materials; the first having an internal origin and having surged out from fissures or dislocations in the earth's crust; the second having an external origin, distributed and deposited most often by reason of gravitational action. We shall study these successively. The sedimentary materials are exceedingly numerous. Their formation, which commenced with the first relief of the globe, continues without interruption to the present time. These rocks may be classified from point of view of their origin which may be established as mechan- ical, chemical or organic. The sediments which have a mechanical origin are called detritus. They are formed from surface rocks united, as a result of their weight, through the vehiwle of atmospheric agents, waters, or wind. They may be loose and unconsolidated or compacted with the aid of a cementing material. Among this class of rocks we have the sands, grit-stones, gravels, conglomerates, etc. The sedimentary rocks of a chemical origin are solidified precipitates. Certain are siliceous like the millstones; others calcareous like certain travertines and tuffs. Gypsum appears to be of this class. Organic sediments fall under two main categories: the chalky and the carbonaceous. Sedimentary rocks may be classified according to the epoch in which they were formed. The following time scale is cited: Modern period Quaternary era — (Pleistocene : Sub-period Pliocene ft Neocene — {Sibepeny od Miocene ___[Sub=-period Oligocene Period Eocene Hbepori od Eocene Sub=-period Cretaceous Sub-period Lower Cretaceous Sub-period Upper Jurrassie Secondary era — « Period Jurassic—« Sub-period Middle Jurassic or Mesozoic Sub-period Lower Jurassic Period Triassic or "liasique" eriod Permian Period Carboniferous Primary era or _ { perio Devonian Palaeozoic Period Silurian Period Cambrian Tertiary era or Neozoic eriod Cretaceous- These sub-periods are further subdivided into stages of purely local occurrence. Similar materials may be formed in two epochs widely separated in age; on the other hand two materials formed during the same time period may differ widely in all their characteristics. The topography may also vary greatly. To give an example of the above we may point to the gentle undulating plains of the "Champagne pouilleuse" and to the strange chaos and disturbance of the rocks to the north of Bohemia in Swiss Saxony. The rocks of these two regions are almost contemporaneous in age but differ widely in their characteristics. In the first chalk pre- dominates; in the second a grit-stone to which the Germans have given the name "Quadersandstein". The eruptive materials, like the sediments, may also be looked upon from a double point of view, that of their physical character and according to the epoch of their formation. The granites have an entirely crystalline texture and are exceedingly uniform. They have been formed under the influence of heat at great depths without exposure to the atmosphere. The porphyritic rocks have a crystalline structure but irregular and with amorphous con- stituents which show that their solidification has been under conditions of agitation. The volcanic rocks are in general amorphous or vitreous. Classifications of these types of igneous rocks overlap, as in the case of the sedimentaries. Chemical action may modify their characteristics profoundly. Sedimentary rocks may undergo a metamorphism which lends them a crystalline aspect. It is only after a severe examination that one is able to classify the rocks of the Archean terrain which have undergone such intense dynamic metamorphism. The materials of the ground give an invaluable clue to ancient geographic and structural forms. Certain sediments may point to a glacial origin, others marine, lacrustal, or aeolian. Palaeontological evidence points to the salinity or freshness of the waters. Eruptive rocks give evidence of dislocations and disturbances in the crust of the earth. ARCHITECTURE OR TECTONICS OF THE EARTH'S CRUST When one is travelling through a mountainous country, especial- ly one whose summits rise above the limits of eternal snows, one is naturally led to think that such a region owes its origin to one definite upwarping of the earth's crust. One must, however, take into consider- ation secondary modifications of the crust; modifications even of such magnitude that they escape our observation by reason of their own immen- sity. Despite the quantity of observations accumulated up to the present time, we have not been able to deduce the nature of the general plan of deformation, and we are reduced to theoretical deductions of which a great tetrahedral deformation appears to be most reasonable. Recent works, and notably those of M. Haug, prove to us that certain portions of the earth's crust are always distinguished by their mobility, while others have had a relative stability throughout all geologic time. The essentially mobile parts constitue the geosynclines. M. Haug has called the relatively stable areas the continental areas. Modifications of the first order are those which correspond to oscillations of the great continental areas. These are developed as a result of enormous lateral pressures developed by the relative play between these great masses. 0 —— 140 “160 Longitude 180 West 160 irom _ uo Greenwich 120 100. 80 gy 6D 40 y a PROGRESSIVE OUTLINE MAP ~N i Wal oh 8 z ‘THE WORLD <4) ON MERCATOR PROJECTION. % $171.8 Y I i ~~. vy ™N J Jr Sa a ae) . ANTONIN TH maa ot NS) SrtmeSm $ 2 ARR: I ST Sa x aps Sri an Tropic of | Cancer be Pans mo ns a — nS A © »? Oe { 3 O PACIFIC CONTINENT _._.. Tropic of Capricorn _ cm fe co STIONS. esignated by a succession of arrows: Fre 2 GEOSYNCLINES AND ion of feathered arrows, == —>> CONTINENTAL AREAS OF THE WORLD (From “L' Architecture du Sol de la France”. Hosen, SHIP : Sr NG-VERSSEL ! ~~ ass een . amlotdmteiel {OAD : stinet, colored pencils or colored inks tains, 'eaus, Deserts, Plains, Moist oleami®, .’lant, and Animal Regions; ., may be designated by shading the lors. Antarctic Circle sesnnes $0 180 180 160 10 120 100 80 IRA ECO OAS CCR LOCH Hy — -n = There are also to be taken into consideration modifications of the second order and their effects to which our attention is especially ~ attracted because they are measurable by the eye. These modifications affect both the continental areas and the geosynclinal areas, but taking in the latter case a special significance by reason of the ease with which such regions are deformed. All deformation of the terrestial crust is the result of a number of elementary deformations or movements. Among the latter we distinguish two types: the fractures or faults and the folds. It is necessary at the present time to recognize a third, the overthrust faults ("les charriages™) of which the works of M. Marcel Bertrand have shown | the frequency of occurrence. Discussion of faults, oblique and vertical; flexures; folds, assymmetric and symmetric and recumbent; fgn-shaped folds beveled by erosion; composite fan-shaped folds, anticlinal and synclinal; overthrust faulting; upwarping by reasom of laccolithic invasion; and discordance of beds of sediment.ry strata deposited upon the upturned edges of eroded, folded beds. SCULPTURE OF THE EARTH'S CRUST The materials of the earth's crust which are exposed to the atmosphere may be broken and split by the diverse causes of mechanical disintegration to which they are subjected. Alternations of heat and cold; varying humidities; freezing which disjoints the most durable rocks when they are permeated by water; the action of organisms, vegetable or animal; certain chemical actions of the atmosphere - all tend to bevel the surface. These products of disintegration may then be transported by action of the wind, of surface waters, subterranean waters, by glaciers, or by the sea. Such forces provide the key to the study of topographic forms. In this work, however, we are more interested in the broad geographic lines. Topographic and geographic detail are governed by two gemeral rules. The first is this: the sculpturing agents have the effect of bringing into accentuation the most resistant parts of the earth's crust ("les agents de sculpture ont pour effet de mettre em evidence les parties résistantes du sol"). The second rule concerns water courses or drainage lines; it is a bit more complex and has need of several preliminary definitions. A water course constitutes a mechanical agent having vital force which it employs in the cutting of its bed or in the carrying of all sorts of detrital material. There is, however, a definite level below which a stream can not cut; this is called base level ("le niveau de base"). The ol ead Of equilibrium is established. The stream then tends to widen its bed upstream. Finally the valleys are widened and their sides leveled gradually. This continued wearing of the ground lowers the relief of the region, producing finally not an absolutely horizontal plane, but a country of exceedingly gentle relief called a peneplain. A relative lowering of base level due to uplift of the region, or perhaps the drainage of a lake which formerly marked the base level or due to other cause,will institute a new cycle of erosion. Such action will account for many modifications in topographic relief. Consequent streams are those which take their courses in the direction of the greatest slope regardless of the attitude of the under- lying beds. The lateral channels of subsequent streams follow the lines of the soft beds. Terraces may be formed as a result of an alternation of hard and soft strata of considerable dip. Streams then will take parallel courses. This is illustrated in the region of Bastern Paris where the attitude of the of the tabular elements is roughly conical, the lines of the water courses consequently converge, and the cornices which terminate the terraces follow concentric lines. Sculpture of an wclined table. 2A Formation of r Cornices, Ihe origin of terraces depends absolutely upon the alternation of resistant beds with soft beds. (La naissance des terrasses depend absol- ument de l'alternance de couches resistantes avec des couches tendres.) When this condition does not exist terraces or cornices are not produced. Terraced countries are readily distinguished on geologic maps by the distribution of the colors in belts generally in chronological order. Territories corresponding to these belts have a simple structure, their detailed topography depending upon the nature of the underlying rocks. Different types of regions are thus formed to which special names have been given; thus we have la Haye and La Woevre in Lorraine, la Champagne pouilleuse and la Champagne humide, le Vallage, l'Argonne and le Barrois. In each of these regions there exists a characteristic small drainage system which joins the general drainage system of the region. Folded Regions:- Such areas tend to establish, in their initial stages, consequent drainage lines. Later subsequent characteristics dev- elope and the rivers follow the lines of easiest erosion. Longitudinal and transverse valleys are formed. MM. Lugeon recognizes that many of the transverse valleys in the Alps have been formed as a result of a series of conjugate transverse series of folds accompanying the main disturbance. Continued erosion in a folded region may produce a veritable "inversion of relief", that is anticlinal valleys and synclinal ridges formed as a result of the differential hardness of the constituent beds. Deformations of the crust of the earth proceed exceedingly slowly. The region of the Upper Vosges is cited as an example of an ancient folded region, reduced to the peneplain stage by the first cycle of erosion, then submerged beneath the sea, covered with sediments, fimally uplifted again and subjected to a new cycle of erosion. In places this old peneplain is exhumed, often the effects of the first folding are seen. GEOGRAPHIC EVOLUTION In considering all we have said regarding the structure and deformation and progressive erosion of the crust of the earth we should be able to learn something of the general processes of evolution of the geo- raphy of the globe. Su L'Acchitectuce du Sol de la Fi Jan.- May \A23 Positions of the Successive Great Continental Folds of the Region of Europe. The natural tendency is to consider the superficial crust as following step by step the shrinkage of the interior core of the earth. This, however, is not the case; the crust has adjusted itself to the re- treating core by sudden deformations separated by long periods of relative quiescence. These great earth movements have been recorded in the lines of ancient continents and in the borders of transgressing or receeding lines. 95081 Snore a work of M. Marcel Bertrand has pointed to three periods of great orogenic activity in the history of the earth. In each one of these periods there has been formed a great line of folded mountains, flanked no doubt by regions of tabular relief which were the indirect consequence of the movement. These folded bands or "rides" have been given the names Huronian, Caledonian, Hercynian, and Alpine and have occurred from North to South in the order named in the Cambrian, Silurian, Carboniferous, and Miocene periods respectively. The formation of each one of these great mountain lines has been a phenomenon of long duration comprising many phases: a preparatory phase, a phase of maximum disturbance, and a con- cluding phase. Studies of lM. Haug of these ancient mountain systems and of the disposition of the geosynclinal amd continental areas have given us the following conception of the history of the European region: A general continental arrangement always the same: two con- tinental areas, one to the north - the continent North-iAtlantic, the other to the south - the continent of Africa ("africano-brésilien"); between these two a sea extending to the east and west following the lines of the Mediterranean, in the center of which is developed a geosynclinal more or less sinuous and ramified and receiwing sediments derived from the neighboring continents. Then followed certain modifi- cations in the general arrangement; at four different periods the Mediterranean region was almost completely uplifted accompanied by the removal into:the mountain regions of sediments previously deposited in the geosynclinal area. Finally came periodic returns of the initial situation , but with the difference that all or part of the mountain area formerly restive was warped up along the continental borders to the north rejecting all the sediments of the preceeding period of erosion toward the south. But this summary does not suffice to give us the details of the history of the continent; in fact the geologic history of central Burope is not that of the Mediterranean area. We shall study more closely the geographic evolution of central Europe, most particularly in the region of France. GEOGRAPHIC EVOLUTION OF CENTRAL EUROPE We have already studied the geologic time scale as deduced from a study of the sedimentary deposits of the different periods; a similar scale may be postulated using orogenic movements as the basis of time reference. Thus on this "orogenic scale" we speak of Hercinian times, the Alpine period, the post-Hercinian period of repose, etc. For the period of duration of the Tertiary or Alpine period the average of many estimates is about three million years. The time periodsof the secondary (Mesozoic) and primary (Palaeozoic) periods are placed at nine million and thirty-six million years respectively. Ihe Primary Era:- 4t the end of the Huronian epoch the emerged land was rep- | resented in the region of Europe by the continent to the North of which we have already spoken; this extended to the north of Norway and Sweden around to North America. In the center of the continent was a shallow sea; certain insular regions and the southern part of the continent were emerged, their borders being determined by the great Huronian folding. The Caledonian period marked an extension of the northern part of the continent toward the south. Silurian sediments were deposited over the area of the present Norway and Sweden, and a new geosyncline developed in the Devonian sea. ~ The most important modification of geographic outline occur- red during the Hercymian epoch; this period marked the emersion of nearly all of central Europe. After a number of preliminary movements, the sed- iments deposited in the geosynclinal depths during preceeding epochs were energetically folded giving rise to the different orogenic wrinkles of the Hercynian system. At the end of the Carboniferous a "Hercymian Central Europe" with its mountain chains, depressed basins, and watercourses had been developed. We possess a very clear notion of the outline of this Hercynian Europej studies of the deposits of that period permit a recon- struction in a certain measure of the location of mountain chains, the direction of their folding, their approximate altitudes, and one may imagine a great series of mountains of the grandeur of the Alps extending from Brittany to Bohemia, and passing through the region of central France, the Vosges, the Ardennes, and all of central Germany. The gen- eral direction of these folds was that of two great curves, one to the south of the ancient isle of France (represented by the Ardennes region southeast of Brussels), the other to the north of Bohemia. A uniformly warm temperature prevailed over the entire globe at this time and the abundance of carbonic acid in the atmosphere was due to the development of an intense vegetation over the new land areas. It was the debris of this vegetation which, carried by the torrents and rivers and accumulating in inland depressions of the continent, gave rise to our deposits of coal. : During the latter part of the Primary era the agents of erosion reduced this Hercynian continent almost to the state of a pene- plain. The Permian period, the end of the Primary era, was marked by important manifestations of volcanic activity. These continued up to the beginning of the Triassic, then diminished during the rest of the Secondary era, which was for the region of central Europe a period of relative repose. Secondary Era:- The breaking up of the Hercynian continent, commenced during the Permian epoch, continued through the Triassic which marked the debut of the Secondary era. Progressively lagoons, then veritable arms of the sea took possession of the major part of central Europe. The insular areas under the attack of erosion were rapidly worn away. The accompanying map shows the approximate distribution of the land areas at the end of the Triassics This general form was maintained throughout the rest of the Secondary era, but with many variations of detail in the outlines of the insular masses, location of shore lines between the northern and southern continents, etc. Certain land masses, however, have maintained their permanence throughout all geologic time. Brittany, Eastern Russia, Central France, Bohemia, and a part of the Western Mediterranean area (which lM. Forsyth Major has called the "Tyr- rhenide") are examples of such "positive" areas. 4 general retreat of the ocean areas characterized the close %5ee pg. #7 “L'Acch du Sol de la France” R0° Su Y 2 'Architectur { France Jan.- May 1923 { innit of wueo of ithe Permian ciodo (Continental areas are ed. ‘ mr of the Secondary era. Zlertiary Era:- The beginning of the Tertiary era was marked by an emersion of almost all of Europe, an emeesion similar in every way to that which occurred during the Carboniferous. Great continental folds were dev- eloped during the maximum phase of this period - the Alpine revolution. Results of this Alpine folding, which erosion has been unable to efface, are today expressed in the great chain from the Pyrenees to the Caucasians, including the Alps, the Carpathians, and the Balkans, with their branches. This mountain revolution occupied a period of great duration beginning in the Eocene with the production of the Pyrenees, and reaching its maximum during the Miocene with the upheaval of the Alps. All of Europe, however, was not affected by this folding. To the north of the zone of folding there extended an almost flat continent where the sedimentary terrains deposited during the preceeding periods were reduced almost to the peneplain stage joining together formerly detached pieces of land. Thus there existed a zone of tabular architecture merging with the zone of folding, and situated in general to the north of the latter. During this time there also occurred a series of subsidiary phenomena. The sea penetrated into certain depressed parts of the con- tinent and deposited its sediments. In other continental areas volcanic eruptions were manifested just as after the Hercynian revolution and lavas were poured out over the land. The continent was not able, however, to maintain itself in this phase. Certain continental areas were destroyed between folds during the Pliocene period. The Mediterranean maritime province, which had almost been obliterated during the Alpine revolution, was recon- structed bit by bit. Quaternary Era:- The Quaternary era marked, during the Pleistocene period, the continuation of the deepening of the Mediterranean zone, and notably the formation of the Aegean sea. But a more important movement occurred in the Atlantic region. The continent was dislocated forming a barrier be- tween the seas of the polar region and those of the equatorial zone. The presence 0f great mountain masses contributed, without doubt, to the extraordinary atmospheric precipitations which greatly extended the glacial domain. All of northern Europe was covered with a canopy of ice analogous to the covering of the polar regions today. The glacial period was marked . by many phases of extemsion of the ice sheet separated by phases of retreat. In the oldest period of extensi on, which was the greatest, the edge of the northern ice sheet descended as far as the limits of the present massive mountains of central Europe. This glacial regime has had a considerable part in the modeling of Russia and of the greater part of Holland and northern Germany. The present geological period, which has succeeded the Pleis- tocene, has seen the resumption of the work gf the agents of erosion upon the land modified by glaciation; it is then a period of wear. The repose of orogenic activity is always relative; perhaps the base which supports Great Britian, Ireland, and France is destined to be broken up. The earthquake tremblors and the manifestations of volcanic activity in certain Mediterranean regions are evidence that the subsidence of that basin has not yet terminated. Other vibrations occurring in parts of central Europe, & MM ¥ as in the region of Darmstadt for instance, lead one to believe that the relative movement of the great earth blocks is not yet completely ended here. It is not at all proven that the phemomenon of folding is. taking place with extreme slowness beneath our very eyes. Certain demivellations of the earth's crust resembling those established during the Jurassic period seem to have been established during the last century; these may perhaps be attributed to tectonic movements. GEOGRARHIC CONSEQUENCES From the above geologic history proceed all essential notions on the sculpturing of the various parts of central Europe. We conclude that the comstruction of the present relief dates back to the Tertiary "era, during which the principal elements were determined tectonically by the movements of the Alpine orogemic phase. Since that epoch the relief has been subjected to erosion, and this sculpture by the agents of erosion, which gives us the picturesque topographic forms that we observe today, may continue toward the monotonous peneplain stage until there occurs another tectonic readjustment. Two types of relief must be recognized as the result of the " Alpine revolution. The first is that directly due to folding; this includes such uplifts as the Pyrenees, the Alps, the Carpathians, the Balkans, etc. The second is the result of the play of large dislocated earth blocks (faulting) relieving themselves from the stress of orogenic movements; This type includes the mountains of Bohemia, cempral France, the Vosges, . Ardemnes, central Germany, etc. In the former type 6f relief the Tertiary folding has been intense having an essential role in the formation of the ‘relief. In the second type, the foldifig has not followed the forms of simple curves and has not had the same intensity perhaps due to the relative play and adjustment of the earth blocks. Here the characteristic form is tabular, in the first type it is folded. All the mountains have been largely eaten away by ercsion. The ‘highest parts of the folded zone have lost perhaps half their altitude, exposing the cores of the folds. The highest parts of the tabular zone have likewise been largely decapitated. Many of the Tertiary beds have disappeared; in places even the Mesozoic beds have been cut away exposing parts of the ancient Hercymian surface. The surface of the earth is then formed 'by fragments of this exhumed late Palaeozoic peneplain. The Rhine plateaux (les plateaux rhémans) and the Thiiringerwald are examples of such areas; they have escaped immersion during the entire Mesozoic time, and afford valuable evidence for the study of the surface of ancient Europe. CHAPTER ONE ~ GENERAL RELIEF FORMS OF FRANCE If one studies the hypsometric form of the land he will notice that the region of France has a symmetrical disposition. Most of the mountains rise around the circumference, elevated like a suite of natural ramparts which commences with the Pyrenees, extends across the Alps, the Jura and the Vosges, and is terminated to the north by the Ardemne plateau. In the interior of this enclosure formed by the mountains and the seas rises the Central Massif . of France. Extending like arms from this central mass are, to the west, the hills of Poitou, of Brittany, and of Normandie; to the south, the Black Mountain (Montagne Noire) and the Corbiéres; to the north the Cote-d'Or, the Platean de Langres, and les Faucilles. There & No RT wl SEA an Bavarian Py MAP OF CENTRAL EUROPE Massive mountains £1 of the Alpine folding Hercynian or pre-H-- = So ig e i \&x % Gale eu —- =p LS are also three areas of relative depression; these are the Aquitaine, the depression of the Rhone and of the Seine, and the Parisian Basin. GEOLOGIC HISTORY OF THE AREA OF FRANCE Primary Era:- Up to the Carboniferous epoch the general situation of the region of France was maintained without any great variations. Except for an insular more or less large in the central region the sea occupied nearly the entire extent. The North Atlantic Continent, after its exten- sion by the Caledonian folding, interests us but little since it extended only as far as the region of Belgium. An island existed to the south of this advance over the area of the French Ardemmes. Important modifications occurred in the Carboniferous period; this period marked the emergemce of all of this territory. At first a number of land areas appeared separated by arms of the sea; progressively these arms disappeared giving place to lagoons having only a remote connection with the deep sea which had retired to the west of Europe. At this time were heaped up beds of sediments which fesulted from a reduction of the relief by erosion. Abundant vegetation was developed upon the newly emerged areas the detritus of which was later to form coal, The action of orogenic movements lessened the importance of these inland lagoons during the period of the Hercynian revolution and a system of folded mountains was developed. Traces of these mountains extend at the present time diagonally from Brittany toward the south of the Central Plateau, appearing again in the north-east in the Vosges and the Ardennes. The formation of coal proceeded over that continental region, favored by the creation of synclinal depressions into which the vegetal debris was carried by the action of running waters. Hercynian France probably extended for some distance into the space now occupied by the Atlantic Ocean, limited to the north by the lagoons the position of which is indicated by the Franco-Belgian coal deposits. A vast system of mountains comparable to the present Alps extended in a sort of V shape from Brittany to the Vosges to Ardemmes. The soil of this territory was composed of a series of Archean and Palaeo- zoic strata greatly disturbed, however, by the Hercynian movements and intruded by eruptive materials which accompanied that revolution. The Permian period, which marked the end of the Primary era, was mainly a period of erosion; local subsidence, however, permitted the formation of new lagoons; volcanic eruptions continued. Secondary Era:- | The Secondary era was for the territory of France, as well as for the rest of Central Europe, a period of relative tranquility. We have seen that this era was marked by a return of the seas on the Hercynian continent and that central Europe had returned to its primitive condition, being reduced to a certain number of insular areas. Shallow seas existed toward the north, with deep waters in the geosynclinal troughs to the south. The region of Frahce was divided unequally into two zones, one bordering the geosyncline to the south and covering the area of the present Alps to the Pyrenees, the other zone to the north largely encroached by the shallow seas. This general plan was maintained during the Triassic, Jurassic, Cretaceous periods with some variations due to slow deformations in the earth's crust. Brittany, the region of central France, and Anglo~-Flemmish | | ground stood above water at the beginning of the Secondary era. During the Liassic (Lower Jurassic) small islands located in the position of the present Vosges ammounced the appearance of a new land which we shall call the Rhine territory (Terre Rhémane). This land area was developed during the Middle Jurassic period thereafter assuming defigite form as an emerged area. Toward the close of the Secondary or Mesozoic era the sea retired and a general emergence took place. Iertiary Era:- The Tertiary era was ushered in with this general emergence and retreat of the seas at the end of the Cretaceous period; and that emergence, like that which marked the debut of the Hercynian folding, was the fore- runner of important orogenic events. During the Eocene and Oligocene per- iods the movements of the earth increased in the geosynclinal region; at the same time the waters invaded certain parts of the northern region, not 80 extensively however as the invasion which characterized the Secondary era. A zone of folding was fashioned bit by bit in the southern region; this was the "Alpine fold", sinuous like the geosynclinal that it traced. The Pyrenees region existed at the end of the Eocene, but it was not until the close of the Miocene that the maximum phase of the Alpine folding was expressed. The France of the late Miocene period had not yet reached the outline of the present time. It occupied a very elongated area extending on one side to the Tyrrhenide, and on the other to England. During the Pliocene, subsidence of the land, announcing the end of the Alpine fold- ing, dislocated the Tyrrhenide and fixed the conditions of the major part of the present shores. Quaternary Era:- The early Quaternary or Pleistocene period brought some mod- ifications in the shore lines, notably at the English Chamnel and the Straits of Dover, as well as some movements on land such as the re-elevation of the Ardennes and eruptions in the central region. On the whole, however, the Quaternary was a period of sculpturing and erosion. The glacial regime modified for a time the work of destruction and gave the country certain physiographic forms, at no time, however, reaching the development that it acquired in northern Europe. The ice sheet extended in effect no further than Holland, and glacial manifestations to the south were confined to the high mountain areas. The present geologic period is characterized by erosional activity accompanied by all its subsidiary phenomena. Atmospheric pre- cipitations have greatly diminished and already a considerable lowering of the relief has been accomplished. HIC CON; From the preceeding summary we see that Hercynian France was worn to the state of a peneplain, covered with water during most of Secondary time, and finally uplifted and given a positive relief during the Tertiary era. This last relief is divided into two zones: a zone of folded architecture, and a tabular zone. The folded part comprises the Pyrenees, the Alps, and the Jura. The tabular zone consists of a certain number of blocks relatively immobile or elevated: Brittany, the central mass, the Ardennes, and the Vosges, and also a relatively depressed block, the Parisian region. We shall briefly consider these two physiographic elemen tse ‘ { - (1) The elements of the folded zone, while all of Tertiary date, are not all of exactly the same age. The Pyrenees seem to have taken their definite form before the Alpine area. The latter was folded by movements which commenced in the Pliocene, while the Pyrenees date back to the Eoceme period. The Pyrenees therefore show greater erosional effects than the massive Alpine region. Not only are the former mountains of lower altitude and the region of eternal snow more confined, but cer- tain characteristics have disappeared; for example the border lakes which circle parts of the younger Alps, do not exist in the Pyrenees. Moreover, the curvilinear disposition of the Alps and the numerous folds which con- tribute to their formation, give these mountains an architecture infinite- ly more complex than that of the Pyrenees. ; The folded zone does not exhibit a good geographic continuity. (2) If we study the relatively elevated blocks of the tabular zone we see that certain areas are undergoing a readjustment of their relief. In Brittany, which is composed almost entirely of ancient rocks, the readjustment has been insignificant. This part of our territory is but a fragment of the ancient Atlantic continent which was spared by all the Mesozoic seas, and which was not dislocated until the debut of the present geologic period. Its feeble relief is nearly that of the ancient peneplain to which this territory was reduced; the events of the Tertiary era have modified it but little. ; The other mountainous regions, Central Massif , Ardennes, Vosges, and their branches, have well accentuated topographic forms since they have been subjected, during the Tertiary era, to a seige of earth movements which have vigorously rejuvenated their relief. In cértain areas erosion has been sufficiently active to strip off all the younger strata and exhume the ancient Palaeozoic substrata with its folds of Hercynian date. It is this substratum which appears in the Ardennes, the southern Vosges, and in the central Massif; in the northern Vosges it is covered with a Triassic crust, while in the isthmus shaped area between the Vosges and Morvan (southwest of the headwaters of the Seine, in central France) the Cretaceous beds appear. Progressive erosion of the ground has had much to do with the sculpturing in these areas. In certain places volcanic phenomena have completely modified the topography; extensions of the Gentral Plateau exhibit this "eruptive architecture". The region of Anglo-Paris is a relatively depressed region lying between the heights we have just spoken of and those which today constitute the relief of English-Cormwall and Wales; a recent division into two parts has given rise to the English Channel. Mesozoic sediments have been carried from the neighboring mountain areas into this depressed regione. The term "Parisian Basin" is in fact a misnomer and serves : only to confuse our ideas of the present topography. The name "Parisian Region" is more apropos as applied to the cemtral part of France which was covered by Tertiary seas, receiving their sedimentary deposits. The geologic history, however, of different parts of this area has varied Just as prevailing conditions have varied; the result is a number of distinct topographic forms. (3) If one examines the depressed regions which separate the Central Plateau from the Pyrenees and from “ne Alps he will find that they are not completely analogous with the Parisian Region. In the latter, £9 which has been protected from the ramming action of the Alpine folding by the Central PEARS the folds are continued only in the form of simple waves. In the two other depressions, on the other hand, mechanical actions have greatly affected the attitude of the strata. In the latterareas the outside flanks have been carried along in the movement of folding, while the flanks that border on the Central Plaseaw have been more or less broken into earth blocks by faulting; with the difference, however, that the Aquitaine being much wider has offered a greater resistance to these actions, its succession of sedimentary beds is therefore much more contin- uous « The several areas mentioned above may be located on the accomp- anying map. (® 192) The general disposition of the hydrographic resources of France ts readily understood after this summary of the physiography. It is quite natural that a large river should follow the Rhone depression between the Western Alps and the Central » and that another should drain the Aquitaine taking its branches from the two mountain masses which frame this depression. The Parisian Region, lacking homogeniety and regularity, sends its waters in many different directions. * % * The consequence of this hasty summary of the geology and Physiography of France serves to show that it is necessary to study sep- arately these several types of regions that we have distinguished. In the following chapters we shall therefore study successively: (1) the Region to the North and North-West; (2) the Region to the North-East; (3) the Region of the South and South-West, that is the Pyrenees and Aquitaine; (4) the Region to the East and South-East comprising the Jura and the Alps, with the valley of the Rhone; (5) the Region of the West; (6) the Central Region, and (7) the coast lines. * % ¥ % % CHAPTER TWO ~- THE REGION TO THE NORTH AND NORTH WEST Summary of Geological History:- We have designated, by the name "Region to the North and North- West", all that part of France which extends siorth from the lower Seine to the boundary of Belgium. In this region we distinguish three natural topographic sub- divisions viz., (1) the region of Western Paris, covered by Secondary or Mesozolc strata; a relatively depressed area, inclined gently, and grading insensibly into (2) the Belgian Region, another relatively low area, cover- ed almost entirely with Tertiary strata; (3) is the Region of the Primary Plateaux; covered by ancient terrains and extending from the Rhineland to the headwaters of the Oise. Before proceeding with the separate study of these three regions it may be well to recall some of the indications that our historical geologic summary has given us on the subject of the evolution of this part of our country. When the Hercynian continent was invaded by Secondary (Palaeo- zoic) seas and dismembered bit by bit, this region to the north and north- west resisted the gemeral subsidence. The lagoons of the Triassic did not advance here until the close of that period; furthermore there ex- isted a territory at that time over what is now the Straits of Calais and the North Sea. The Anglo~Flemmish territory subsisted, with some changes in contour, during Jurassic time when the seas covered the greater part of the Parisian Region. This same condition prevailed during the Lower Cretaceous period, and it was not until near Middle Cretaceous that the seas succeeded in invading all the country with the exception of some islands and the Rhine Territory to the east. After the general emersion which characterized the debut of the Tertiary, the Eocene and Oligocene seas returned over the region but with intermittences and very variable shore lines. Then they re- “tired to the north, returning from time to time in small transgressions which, in the Belgian Region, were prolonged during the Quaternary era. The result of this varying geologic history is that the region to the north and north-west does not by any means show in all its parts a complete succession of post-Primary strata. It is probable that the Ardennes plateau has never received sedimentary deposits since the Primary era. We must also take into account the tectonic variations in this region. During Hercynian times, all the country to the North had a folded structure. Mountains more or less high existed, and it is their folds, worn down to a peneplain, that constitute the sub-base upon which the post-Primary sediments were deposited. Escaping later folding actions this region became a zone of tabudar architecture. Then simple undulations were produced having the planimetric disposition of the ancient Hercymian folds; these reached their greatest development during the Tertiary, in the Middle Miocene. Since that time see-saw movements have slowly pro- ceeded, elevating the region of the Primary Plateaux and gently inclin- ing the Belgian Region toward the north. It is from these "see-saw" movements (mouvements de bascule) that these areas have derived their dominant characteristics, while in the Region of Western Paris simple undulations have played the most important role. REGION OF WESTERN PARIS (Western Parisian Territory) General Considerations:- The western part of the Parisian Region extends from the English Channel to the lower end of the Oise. For the most part this territory comprises a Cretaceous plateau whose surface is hidden in places by a Tertiary skin and by some Quaternary deposits. The Tertiary covering formerly extended over this entire region to the north of the Seine it has now been almost entirely removed except in a few isolated spots. To the south it is more important, but even here erosion has largely cut into it, and Cretaceous rocks appear in the floors of nearly all the valleys. Tectonic influences have also modified this region to some extent. There seem to be two systems of undulations, one having a general N.W. - S.E. disposition, the other at right angles to this. The former are by far the more important, the latter being expressed in only two large synclinal depressions. The present topographic disposition is determined largely by the positions of these undulations. The first group expresses itself in Villeneuv \ ° 9 M ok ST. FRANCE ” a Nanterre [27 2), ers Sant Shaler a, NORTHERN PART. SCALE OF STATUTE MILES EY VE Ems py rm - 0 10 20 30 40 50 60 7 80 90 100 SCALE OF KILOMETERS ==T = 1 = 70 10 Ww 0 0 10 I y Important towns are shown in heavy face type Railways shown thus Canals mm PARIS AND VICINITY SCALE OF M'LES 1 2 A C O.de la y ALDERNEY CHANNEL » © pSARK ISLANDS Br, a 1.DE CROIX, erin ER Le 0 ZF 1 oye dR 4 Yer Le ’ Pte. de la Coubre Gironde 2° from D 1° Greenw, E . G East 2° from H . 3°Greenw. J - L 6° M 1 COPYRIGHT, 1906, BY DODD, MEAD & CO. = a the depressions of the Perche (le Perche) and lower Normandy (la Basse Normandie), described later under the chapter on Western France; the second forms the Pays de Caux north of the valley of the Seine, and southern Picardie; the third forms to the north, Artois and northern Picardie. The system of undulations ruming at right angles to these determinesthe depressions of the valley of the Oise and that of the Straights of Calais. Details of these Regioms:- The area we have called the Pays de Caux and southern Picardie includes also the Pays de Bray, Vexin, Beauvaisis, and le Noyonnais. The differences noticed in the physical aspect of these diverse territorial elements are due to variations in the nature of the rocks. The chalk, which in general constitutes the rock of this region, is very permeable and unresistant where not covered by a Tertiary crust. The fertility of the soil of this region depends upon rock materials other than this chalk. Anticlinal undulations and erosional activity have given this region a stratigrapny somewhat similar to that of a region of folded mountains. Thus in the region we may see Cretaceous limbs on an eroded anticline bordered on the inside by Lower Cretaceous limbs, with a small Jurassic dome in the center. The impermeability of the Lower Cretaceous and Jurassic beds has favored the development of pastures and Woods “in these areas. We see then a sort of oasis in the center of an area of chalk. To the north of the Somme, Northern Picardie comprises several small districts: the Vermandois, the Amienois, the Santerre, and the Ponthieu, more or less different by reason of the various Tertiary sands and clays which cover the beds of chalk. The Boulonnais and the hills of Artois mark the boundary of the region of Western Paris. Boulomnais, to the west, is elevated as a sort of dome, a reappearance of which may be seen in the English region of Wales. Here the Hercynian sub-basement series is exposed. Iurther east the hills of Artois border the region of Belgium. Examination of the Hercynian substratum shows that Tertiary movements have only served to expose the more ancient dislocations. General Remarks on the Hydrography:- The hydrography of the Western Parisian Region has found the origin of its principal lines in the structural disposition of the region. : The Canche, the Authie, the lower Somme, the Bresle, the Bethume, and the Therain all take their courses in concordance with synclinal undulations. The trace of the Oise appears to have been deter- mined under the more or less direct influence of transverse undulations. The vast depression occupied by the Somme ifidicates that this river once had a much more important role than that which it plays at the present time. The entire system of the Aisne was probably once included in the Somme drainage until the latter was beheaded or captured by the Oise. THE BELGIAN REGION General Considerations:- The Belgian Region borders the Western Parisian region; it was without doubt at ohe time undulating like the latter. Tilting movements have, however, given this area a plunge toward the NE and 16 have permitted the recent sedimentary deposits to obscure the undulations which can be seen only in the inmédiate vicinity of Artois. This territory may be divided into several different regions according to the respective ages of the rodks. First we have the maritime plain with its Quaternary terrains; then Flanders and the Brabant covered with Tertiary terrains; the Hainaut where the Primary or Palaeozoic sub- stratum is exposed; and lastly the area toward the Parisian Region which is entirely covered by chalk. The hydrographic system is in general toward the NE follow- ing the general tilting of the land. Details of the Several Districts:- The Maritime Plain is below sea level in nearly all its area, being separated from the sea by a line of dunes. In certain parts, the "Moeres", there exist great Swamps composed of varied Quaternary terrains. Where the sea has invaded due to a local lowering of the land, or simply to a rupture in the line of dunes, we find marine sands. During periods of tranquility peat and clay deposits have been formed constituting the fertile areas, alternating with the deposits of the sea. In Flanders the Tertiary terrains appear forming a plain, for the most part argillaceous, ani marked by a number of small eminences called "monts". These latter are snady buttes which have been elevated by differential erosional activity giving the region an "inverted relief". In Brabant a mantle of alluvium covers the Tertiary deposits. In the Hainaut the Hercynian substratum appears, elevated by the gen~ eral tilting, and by the anticlinal undulation of Artois. Le Cambresis, l'Ostrevant and le Gohelle constitute the part bordering on the Parisian region; here the rocks are of Cretaceous age. The ancient substratum which appears here and there in Belgian Hainaut, and only a short distance below the surface in French Hainaut and on the crest of the undulation of Artois, presents a zone of rich coal deposits. These coal beds were deposited in a strait which extended near Westphalia in the Carboniferous epoch. Two fegtures characterize this Franco-Belgian coal region; these are the great fault which marks the over-riding of the barren schists upon the coal measures, and the "cran de retour" which separates the most dislocated beds frem the regular strata. : PRIMARY PLATEAUX General Considerations:- The Primary plateaux extend from the heart of Germany as far as the river Sambre (a branch of the Meuse south of Brussels). The ancient Hercynian pemeplain is exposed throughout their entire extent a part of which was never covered by sediments since the end of the ’ Primary era, the rest of which has been stripped of its Secondary sed- iments by erosion accompanying the movements which have rejuvenated the relief in a relatively recent epoch. To the West of the Rhine these plateaux comprise three areas: Hunsriitk between Moselle and Nahe; Eifel to the north of the Moselle; and Ardemme. All #f these territories have a feeble relief the only irregularities corresponding to differences in the hardness of the rocks, the altitude varying from 400 to 650 metres. The soil, often impermiable, resists culture, and nearly all the land is covered by forests and peaty swamps which have been called “"fanges". The valleys in this plateau region are sinuous but steep sided. The continuity of these Primary Plateaux is interrupted by two large gulfs where the neighboring regions intrude finger-like. These are the Gulf of Bonn, by which the plains of northern Germany ex- tend southward to this point, and the Gulf of Luxembourg where the Triassic terrains of Lorraine extend in a point to the north-east. General Remarks on the Hydrography:- All the waters of this area are drained into three great collectors which traverse the region; these are, the Rhine, the Moselle, and the Meuse. These water courses run in entrenched meandering paths, reminiscent of the elevation of the ancient peneplain. The Moselle is distinguished from the Rhine and the Meuse in that it takes a course consequent upon the recent undulations which were formed in the traces of the ancient folds. The Rhine and the Meuse run transverse to these tectonic structures. The banks of the Meuse appear to be less deeply émtrenched than those of the Mosellej the elevation in the region of the Moselle then is probably of older date than that along the Meuse. The Gulf of Luxembourg is simply the name applied to the extension of the Triassic rocks into the Primary plateaux, marking the encroachment of the seas of Lorraine toward the north. CHAPTER THREE - REGION 10 {HE NORTH-EAST We shall group under the name Region to the North-East all the territories which extend from Paris on one side to the Rhine and the Jura on the other. Geologic History. Great Geographic Divisioms:- At the end of Hercynian times this region was covered by mountainous masses developing their folds from the SW toward the NE. At the end of the Primary era this relief had been gradually reduced to the state of a peneplain by the process of erosion of the higher lying areas and a filling of the depressions by detrital deposits of the Permian epoch. Then followed a gradual dislocation of the Hercynian peneplain; slow subsidence of the land caused the greater part of this area to be submerged leaving only a few islands subsisting. At the same time eruptive materials were extruded from fissures in the earth. This zone of sinking, in which our entire region to the NE occurs, and which may be regarded as being established at the close of the Triassic period, extends all over northeastern France and into central Germany. Triassic sediments are found lying unconformably over the old folded Hercymian series. During the first part of the Jurassic period this condition of submergence remained practically the same, but toward the end of the Middle Jurassic the region was modified notable by the emergence of a large area - the Rhine Territory. This area comprised the present Alsace, Lorraine, Swabia, and the country bordering on the Rhine. The Upper-Jurassic and later the Cretaceous seas cut through this Rhine Territory a sort of Strait which has been called the Morvanno- Vosgien Strait; the width of this marine communication varied greatly throughout the countless centuries of the Secondary era. Toward the end of Secondary or Mesozoic era a gradual emer- gence took place over all of central Europe. Orogenic activity accompanying the Alpine revolution gave rise to two great depressions in this area, one in the location of the present upper valley of the Seine, the other in the central part of the Parisian region. These two ancient depressions, separated by the line locating the former Morvanno-Vosgien Strait, drain their waters in two opposite directions. Before the close of the Tertiary era the Parisian region was elevated; the Upper Seine emerged with the debut of the Quaternary. : This Region to the North-East is then divided into three distinct geographic units: the Rhine territory, the depression of the Seine, and the western Parisian region. The Rhine Territory:- As we have seen, it was toward the middle of the Jurassic period that the Ehine Territory emerged. The following geologic colum is identified in the region of northeastern France: - Portlandien - composed in general of compact calcareous beds. Upper Kimeridgien - marls and unresistant calcareous rocks. Jurassic Series | Sequanien durable calcareous rocks. Oxfordien & . composed of clays and calcareous rocks, Callovien generally soft. Bathonien - composed of marls overlying calcareous beds Middle Jurassic in varying proportion. Bajocien - composed generally of hard calcareous rocks. Lower Jurassic | UPPer Lias - composed generally of marls. Middle and or Liassic Lover Liss in general sandstones or calcareous beds. Keuper = composed entirely of marls. Triassic Muschelkalk ~ calcareous shell beds. Triassic sandstones, having at their base the Vosges sandstones and overlain by the ngres bigarres" (variegated sandstones). This Rhine Territory has a simple geographic aspect as it has never passed through any intense orogenic action from the time of its formation. During the Eocene period a great longitudinal depression, having a general N-S direction was formed in this area. This depression was deepened bit by bit until the Oligocene period when it was occupied by an arm of the sea, which cut the territory in two. At the same time, as a sort of reflex orogenic action, several earth blocks were uplifted, forming the heights of the Vosges and of the Black Forest, and the slopes of Lorraine and of Swabia against which these are set back respectively. The general structural lines of this region were fixed at the end of the Oligocene period. Since then their details have been modified by the agents of erosion. The highest parts of the Vosges and the Black Forest have been attacked and stripped of a great part of their Meso- zoic covering; in certain parts the ancient Hercynian surface is exposed. The less elevated regions of Lorraine and Swabia have taken a terraced topography governed by the inclinations of their beds. The lowest areas still show marine Tertiary and fresh-water Qauternary deposits. \odtt AY $0>° CAVX 7” S / D, Seine INFERIEURE 4 < © { 4 Ne, 3 % i fu) © 2D 2) Roc Hones 3 ooed 49 \ » A Te 2 nk s : , M 7 N T R x p por : Af 3 ef Fone, PE “Te, renbble of , or! J A S S 2 re Fa, <® i ; l r, 3 © . § aT C ‘Ms Sis “ BN. { RCaux O FR Eo i ~ ~/ fa ce OL “DIFdogne R. ed yp Cen RAL 2 / % ; [~ Oo { R ro ey eM eevee t fi oy 4 3 » ¢ 5 pn SET Vials ~ “ i% y 0 kA v ~~ s ’ Nh ; | a Foe i Ph 2 RE Fi Tn, “k Ri << | reto S £2, i ir i ot J . i NB Fo eee Ge oy | aa YW Fle. OF. YI RINON XQ (0 sii vy £m ihe Ye oF i 0° . pon, / ond ot : d £ i 3, of CF Nam fos Cay, , Oh NS A CC FRANCE Le TONS Gen - With Contour of 1000 ft. \ R KE A dr if GES G Conic Projection Scale 76.26 mi. to an inch Sth z A i S Tew q : MAP TO ACCOMPANY REPORT oN - XT Tx Roussui.on “I' ARCHITECTURE Du Sou De ua France S Pa , tial Ang np — ——————————— N ° Geel. 204 Jd Howard Tinkhan : ( Ihe Vosges. The Mountains of Palatinate:- The mountains which rise at the west of the Rhine depression have a varied aspeét due to the effects of erosion and differential orogenic activity. In the central part the Jurassic and Triassic beds have been eroded off of a portion of the area leaving the Hercynian substratum exposed, and constituting a special mountain zone - the Crystalline Vosges. On the western flank of these Crystalline Vosges, erosion has not removed the Jurassic sediments or the lowest beds of the Triassic, so we have a new zone - the Sandy Vosges ("Vosges greseuses"). Finally, to the north of the depression of Landstuhl extending to the valley of the Nahe the ancient substratum reappears, this time represented by Permian beds intruded by eruptive lavas; this district is called the Pfalz-Gebirge or the Mountains of Palatinate. The Crystalline Vosges, the Sandy Vosges, and the Mountains of Palatinate are then the natural divisions of mountains which dominate the plain of the Rhine. The High Vosges: - In the crystalline Vosges we find anticlinal valleys and synclinal ridges in the ancient Hercynian substratum, an inversion of relief with the new cycle of erosion. In the sandy Vosges, on the other hand, the topography is very uniform and is concordant with the structure of the gently inclined strata below. ‘ : In the area of the Sandy Vosges we find the forest d'Epinal, the woods of Rouges-Eaux, and the forests of Mortagne, of Celles, and of Dabo. The topography in general is rounded, in places sharp. These mountains rise above the limit of forest vegetation into a zone of stunted shrubs. In a number of places the impermeability of the soil has determined the formation of peaty marshes; these are the "faignes", analogous to the "fagnes" of the Ardennes. Traces of glacial activity have modified the topography throughout. The crests of the High Vosges seem to line up in three dis- tinct lines, an effect due to the influence of the ancient Palaeozoic fold- ing. Certain effects of differential erosion may be seen throughout. As to the water-courses, certain of their valleys are oriented under the influence of the Palaeozoic folds or Tertiary structural lines, others take transverse courses, simply following the general slope. The Lower Vosges:- The Lower Vosges form a part of the mountain zone which is narrower and of lower altitude. Their altitude ranges from 400 to 500 metres, their width about thirty kilometres. The topography is simple; the eminences are entirely formed of hard sandstone. The higher elevations grade concordantly into the plateau of Lorraine, but terminate abruptly on the border of Alsace under the influence of a great fault. The Mountains of Palatinate:- In the Mountains of Palatinate the ancient Hercynian sub- stratum is again exposed. In this case the rocks are of Permian age dep- osited in lagoons; decaying vegetable matter of that epoch has given us the coal basin at Sarrebrtick.. This region is much faulted and marked by igneous intrusions (mélaphyres). Lorraine: ~- Lorraine is that territory which lies between the Vosges, the Ardennais plateaux, the Faucilles, and the Meuse, in a word it is ! all that country which is drained by the Moselle as far as Treves. The structure of this region is very simple. The Mesozoic sediments, deposited during the first part of the Secondary era upon the sunken Palaeozoic base, are inclined gently toward the west, broken by only a few faults, and folded by the synclinal undulation of large amp- litude which has already been mentioned. In the eastern part of Lorraine the rocks are of Triassic age; in the western part the beds are Jurassic. This division into Triassic Lorraine and Jurassic Lorraine corresponds to an important change in topographic form. The middle and upper Triassic (Muschelkalk and the Keuper) strata offer uniform resis- tances to erosion and have therefore developed a rounded undulating topography. The Jurassic beds, on the other hand, present an alternation of hard and soft rocks which has caused the development of terraces terminated by cornices putting in evidence the most durable strata. The hydrographic system of Lorraine drains in gemeral toward the north. This hydrographic system has been continually modified during the successive phases of the general sculpture of the region. It is evident that the river Moselle once joined the Meuse at a place near the present location of Nancy. The former river, however, was captured by the Meurthe and its course diverted a little east of north. The Moselle is now the principal drainage line of this Lorraine area. This system of the Meurthe and the Moselle traverses successively beds of Triassic, Liassic, and Middle Jurassic age, encountering a variety of topographic forms. HIGH VALLEY OF THE SAONE The general geologic history of north-eastern France shows us that the region occupied today by the upper valley of the Sadne was largely covered by the sea during all of Mesozoic time. In early Sec- ondary time these waters extended freely toward the north; later the emergence 0f the Rhine territory severed this connection, the southern seas connecting with those of the Parisian Region only through the Morvamno-Vosgien Strait. The waters over this area were shallow, the Hercynian base extending beneath as a submarine platform, analogous to that platform which extends today under the Gulf of Lyon from Port Vendres to Marseille. On this platform were deposited the Triassic, Jurassic, and Cretaceous sediments. The dawn of the Tertiary era saw a new emergence of this territory of the Upper Valley of the Sa®ne. Great orogenic movements in thé Tertiary gave this territory an architecture which has never been modified since. The characteristic feature of this structural disposition was the establishment of a great depression, which may be considered the counterpart of the relief of the Jura fold (to the east). This depression had acquired its form before the close of the Oligocene epoch, but sinking continued up to the debut of the Present era. Agents of erosion are now modifying this topography. The Upper Saone constitutes a depression surrounded by areas relatively elevated during Tertiary times. These surrounding "facades" are: to the east, the meridional facade of the Vosges from Belfort to Epinal; to the north, Triassic Lorraine from Epinal to Bourbonne; to the northwest, Jurassic Lorraine and the Faucilles Hills; to the west, the Plateau de Langres and the Cote d'Or; to the southwest, the Morvan. Many faults characterize these surrounding regions. 20 nc AOA Fe 21 EASTERN PARISIAN REGION The eastern part of the Parisian Region would, at first glance, appear to have a simple concentric structure with an absolutely convergent hydrographic system. This is, in reality, a very complex region which pre- sents a number of areas of very different aspects. We shall first sum- marize its geologic history. ; We have seen that the end of the Jurassic period was marked by an emergence which elevated part of the Rhine territory, leaving the region to the west still submerged. Similarly at the end of the Cretaceous another emergence occurred giving the western part of the central Rhine region and the eastern border of the Parisian region their land forms. Finally, in its turn, at the end of the Tertiary the central part of the Parisian region was elevated. re Thus we see that the Western Parisian region had its geograph~ ic formation in two stages, the first at the end of the Cretaceous and the second at the end of the Tertiary era. In this way, two zones have been formed, a central nappe of Tertiary terrains and a peripheral zone of Mesozoic beds (toward the east). Under the influence of erosion each of these has been largely reduced, the latter to a greater extent than the former, due to its greater age as a land form. Topographic Characteristics:- The Secondary peripheral zone, formed at the end of the Cret- aceous period, has been influenced by certain events of the Tertiary era which have had a marked effect on the topographic design. The principal of these events has been the elevation of the border regions, like the Central Plateau and the Primary Plateaux, and the sinking of the central part where the Tertiary waters returned in a sort of depression, result- ing from a simple down-warping. : This topographic structure has resulted in the establishment of a hydrographic system with its principal branches convergent, also the formation of a certain number of roughly concentric terrasses terminated by cornices, putting in evidence the most resistant beds. If now we examine the conditions which have determined the topography of the Central Tertiary Nappe we encounter further complexities due td the varying events through which this territory passed before its definite emergence. A number of successive transgressions and subsidences of the sea has given rise to an extreme variation in the succession of the sediments, and consequently in the nature of the soil. A brief summary of the Tertiary history of this area is as follows:- Pliocene ~ Definite emergence Miocene - Invasion of the central border (Blaisois) by a Tertiary sea coming from the West. Era Continental phase of the lake of Beauce. Oligocene - Marine phase of the Fontaineblegu sands & gravels. ‘Continental phase of the Lake of Brie. Eocene Diverse marine invasions coming from the North. The sketch on the following page indicates the structure (dip and strike) of the strata, and the drainage in this Central Tertiary Nappe and in the Secondary Peripheral Zone. The shaded areas indicate the eastern margins of the Tertiary slopes. PARIS 6) ‘ iy / ~ \ 7° ‘ Ss = - . / NN / gH) 7 a ‘ / bi SLC / / / ~ A ’ i / / ’ © / @ 7 2 / > y / / qa , 7 / < o - / / / oe Q 2. ’ = s / 2 ’ 7 / 7 oY / - / » 7 PAY Zz s < / s ON 7 From L'Architeciure du Sel de la France” Pa 42. The slope which terminates the Tertiary nappe toward the east, and marks the boundary of the "Ile-de-France" is of heterogeneous character, and has been formed in a number of different stages. In this resepect the Tertiary area differs from the Secondary Peripheral Zone, where the cornices which terminate the Jurassic or Cretaceous terraces are homogeneous, and put in evidence the mest resistant strata. The Tertiary beds in le Gatinais francais, for example, are composed of the Beauce limestone of Upper Oligocene date, while the rocks between the Marne and the Seine are of Lower Oligocene age, the Brie limestone; in le Soissonnaid and le lLaomnais the summits are composed of the most resistant beds of the Eocene stage. Each cornice of the Secondary Zone presents a certain uni- formity of aspect; the Tertiary cliffs, on the other hand, present greatly varying forms. Certain parts of the Tertiary area have been given special names; thus we have: la Montagne de Reims, north of the Marne; the Heights of Craomme; and the Massif de Saint-Gobain between the Aisne and the Oise. The relief is greatest in la Montagne de Reims, the heights rising to about 150 metres above the Cretaceous platform. ~ The three main drainage lines of this area are the Seine, the Marne, and the Aisne, their courses, with the smaller ramifications, being determined to a large extent by the structure and the nature of the beds: over which they flow. Le Moyvan:- The Morvan is an elevated area between the Parisian Region and the Upper Valley of the Saone. It is an uplifted fault block formed as a result of movements accompanying the Alpine Revolution of Tertiary date. In this area the surface of the ancient Hercynian pene- plain is exposed where it has been stripped of the Secondary sediments. Under the attack of erosion, and due to the effects of varying rock resistances, a variety of irregular forms have been produced. Coal deposits are found in the Permian rocks of this area at Epinac and Autun, to the north, and at le Cremsot, Blanzy, and Montchanin to the south. The Cote d'Or of Jurassic rocks borders the Morvan on the east. To the north is 1l'Auxois, separated from the mass of le Morvan by a depressed zone where the rocks have been eroded as far as the Liassic strata; this zone is called the Terre Plaine. At the western border of the Morvan extends le Nivernais, a region of complex struct- ure due to its abundance of faults; these faults group themselves rough~ ly in three lines, extending in a gemeral N4S direction. As a result of this fault orientation three distinct bands of terrains are exposed; thus we find the ancient sub-stratum in the most eroded central band - the "pays de Saint-Saulge", an area of porphyritic rocks; to the east and the west are Bazois and Amogmes, respectively. The waters of the Morvan drain into the Loire, the Saone, and the Seine. The drainage is superimposed, the streams being con- sequent with respect to the slope of the Secondary terrains, emtrench- ing themselves more deeply at the present time. x % % » CHAPTER FOUR ~- REGION TOWARD THE EAST AND SOUTHEAST General Considerations:- In order to understand the geology of the region toward the east amd southeast of France ome must have a certain notion of the system of the Alps. The discoveries of M.Suess with regard to this mountain area are most distinguished and have served as a basis for all sub- sequent studies. The unity of the Alps is not strict. Preparatory move- ments occurred in the Secondary era, and during the Tertiary all parts of this mountain system did not acquire their shapes at the same time. The Pyremees existed at the end of the Eocene period, whereas in the Alps tectonic movements did mot stop until the Pliocene. The architecture, being of the folded type throughout, offers different sculpturings which distinguish certain chains from each other. For the Alps the idea of unity must be abandoned. The massive mountains which we call the Alps commence near Genoa at the pass of Giovi where they come in contact with the Apemnins, and end at the Danube where the declination of the ranges forms the plain of Viemna, reappearing further east to form the Carpathians. It is necessary to divide the Alps into two parts, the Eastern Alps and the Westerm Alps. ( In the Eastern Alps the distribution is symmetrical and presents a strip of igneous material (crystallophiliem) surrounded by Secondary amd Tertiary terrains. In the Western part the igmeous zone &oes not have this axial position and is flanked only at the exterior of the arc which it describes. The Eastern and Western Alps may be divided by a line extending from the Lake of Comstance to Lake Come. M.Suess has shown that the Easterm Alps are not homo- - geneous but are formed by three very distinct elements, viz., a northern chain folded toward the north, a southern chain folded to- ward the south, and an intermediate chain which is older than the Tertiary folds, and exists as a foreign area in the midst of the other zones. The northern chain finds its continuation in the Car- pathians, while the southerm chain is nothing but a prolongation of the "Dinarique" folds. The central chain is largely the product of volcanic eruptions and is called the “chaine Carmique". Recent works bring doubt as to whether the Alps may be strictly divided into an Eastern and Western division. It is hard to say where the Eastern Alps commence and where the Western Alps end. Geologic Evolution:-~ Going back to the Hercynian epoch one sees that the region of the present Alps and the valley of the Rhone was a part of the folded mass to which also belonged the central part of France. Observation of the ancient sinking shows that a synclinal depression of almost N=5 direction advanced as far as Vienna, reminding us by its location of the present valley of the Rhone. When the Hercymian continent was dismembered this terr- itory, of variable dimensions, that remained was given the name of Ilot Central de la France, and there existed a band of islands in the position of the present Alps. During all the long Secondary times a marine trough ex~ tended from north to south more or less near the Ilot Central. leso~- zoic sediments were deposited here. Numerous deformations also occur- ed in the Alpine region during the Secondary era; their common trait has been to maintain almost permanently the geosymclimal in the most westerly part of the Alps. As a result the sediments that accumulated in that part had a muddy or mirey nature, while those in the neighbor- hood of the Ilot Central or near the massifs of the Italien fromtier have the character of detritus. This difference in the nature of the material is important to note since it has naturally had its effect upon the sculpture under the agents of erosion. In the Eocene period, after the general emergence that took place at the close of the Secondary era, the great folding movements commenced. During the Miocene epoch the present Alps took their form immediately after great horizontal movements. The Pliocene period saw nothing more than a few minor . movements of the ground on the immediate border of the valley of the Rhone, yet enough to admit the sea as far as Lyons in the mammer of an elongated fjord. In resume, the Western Alps were formed at a phenomenon of very long duration. Prepared by the Secondary era and the first part of the Tertiary era, they did not take definite form until the end of the Mioceme period, embracing at that time, in its architecture, the architecture of the Jura. Since the events which gave birth to this mountain mass much of their altitude has been lost, and we see now, figuratively, only the ruins of the origimal picture. Major Divisions:~ We shall study separately: the Jura and tha valley of the Saone; the Alps; the Basse Provence; amd the valley of the Rhone. Ihe Jura:- The relief of the Jura rises between the valley of the Sadme and the Swiss plain, thus occupying an anticlinal position between these two great tectonic depressioms. In this region we find fan-shaped folds their amplitudes diminishing from east to west. This territory is bounded om the east by the Swiss plain; on the north by the Trouee de Belfort. Om the westerm border the Jura is limited by numerous faults at the valley of the Saome. Architectural Distribution:- The tectomic structure of the Jura is simple as compared with that of the Alps. An altermation of hard and soft Jurassic strata is charadgteristic. In the southern part, the ridges of the Jura have a N-S orientation, changing to SW-NE in the central part, and E-W in the northern Jura. Crossing the Jura from ezst to west one encounters three zones which differ more or less with respect to the intensity of their folding. These are, (1) the High Chain, (2) the zone of plateaux, and (3) the zome du Vignoble (vinyards). In the High Chain the folds are most prominent, the faults of secondary importance. In the zome du Vignoble the folds are very accentuated accompanied by a great number of important faults. This Zone acquires its greatest width near Salins where as many as five separated continuous amticlinal folds may be distinguished. Mention should be made of the basin of Ddlémont, a syn- clinal depression where are found conserved the lacustral ami marine Tertiary sediments deposited before the definite folding of the chain. Sculpture of the Ground:- The relief of the Jura has already been singularly mod- ified by the work of erosion. The tops of the folds have disappeared exposing underlying older beds. A topography amalagous to that of the Eastern Parisian region has been developed as a result of the variations in the resistances of the strata. Im this way a simply folded architecture has developed a complex topography. Monoclinal and anticlinal valleys are common. General Remarks on the Hydrography:- The fissures and the porosity of the calcareous rocks that abound in this region, the grottoes and subterranean cavities fagilitate the underground filtration and passage of wager. The direction of the different rivers of the Jura is in general the disposition of the strata. The great symclinal folds comstitute in effect natural drainage lines. The Ain and the Doubs Rivers are the principal collecters of the region. Most of the waters of the Jura finally arrive into the Rhone; the latter going around the mountain of Saint-Benoit enters the Saone valley. A number of lakes characterize the Jura depressions. (The Lake de Bourget, among others, has a complex geologic history; it has been much further north, traversed at that time by the Rhone. Marginal Zones:- On the east side of the Jura is the Swiss Plain, in reality quite disturbed, but which derives its name as a result of the contrast with the surrounding mountainous areas. The topographic characteristics here are largely dependent upon the work of the agents of erosiom. To the north, the border of the Jura is heterogeneous; this region is called the Trouee de Belfort or preferably, by M.Vidal, the Porte de Bourgogne. The depression here is a compos ite territory which is the gateway permitting the passage of the domain of the Rhine into that of the Rhone. Two very different zones, the "zome sous-vosgienne" and the "zone pre-jurassienne" make contact in this area. Further east these regions give place to two other distinct areas: 1'Ajoie or Elsgau with a Tertiary base but almost entirely cover- ed with ancient alluviums; and le Sundgau where the Tertiary is more exposed. : : To the northwest of the Jura, the faulted zone of Vignoble comes in contact with the plateaux of Northern Franche-Compte, the bor- ders of which are much broken. To the west, the folded Jura is abruptly terminated at the depression of the Saone. ZHE ALPS The nature of the French Alps differs greatly as one goes from the Savoie toward the Mediterranean. To the morth are abundant waters and vegetation; in the south the climate becomes very warm in summer. Forests do not exist except in small areas; the rock is largely barren. General Architecture:- M.Lory, im studying the architecture of the Western Alps, divides this mountainous territory into two dlstincg zones, one extermal, the "region of the Sub-Alpine chains", the other intermal, "the region of Alpine chains". These zones are differentiated by the nature of their constituent rock materials, and are separated by faults which have played a very important role in the gemesis of the present relief. Close observations have shown that what were first presumed to be great faults were in reality more often "plis-failles" or stretch- ed-out surfaces of the beds. As a result we find that the earth sub- sidences have not played such an important part as was first thought, but the principal traits of the architecture of this chain must be attrib- uted to tangential efforts amd to folding action. M.Lory describes the Western Alps as forming by their folds a great composite fam. M.Kilian shows that this fan was flattened and deformed by the superimposition of great mappes of sediment that, coming from the east, flattemed out all the aboriginal folds. Erosion has caused the disappearance almost everywhere of the covering mappes coming from the interior of the Alpine arc, as well as the groups of the aboriginad folds themselves. The Alps expose to us today the hearts of these aboriginal folds. Let us traverse these mountains from the plain of Piedmont to the valley of the Rhome passing through Gremoble and mote the variatioms in aspect of the mature of the ground. At first we encounter only igmeous rocks appearing directly on large stretches of the massifs of the frontier, or masked by a mantle of lustrous schists more recemt through which eruptive rocks ("greem rocks" or greemstones) project in many places. These terrains form a zone of isoclinal architecture inclining toward the east to which is given the name the "zone du Mont Rose™ or "zome du Piedmont". After the zome of Mont Rose comes another zome, the "zone du Brianconnais", having a very differemt aspect from the preceeding ome. The strata here are much folded. : Next comes the zome du Mont Blanc where the folds "seem to have takem the aspect of a vibrating rope". Finally we arrive at the most exterior zome of the Alps. Here the ancient terrains are entirely obscured and Secondary terrains omly appear, usually not older tham Upper Jurassic. The Cretaceous plays a very preponderant role. Let us briefly study the tectomic characteristics of these sev¥eral zones. The first, that is the Alpime zones, are designed so as to form an immense composite fam. The Carbomiferous part of the Zome du Briancomnais constitutes the axis of that fam, while the flanks are formed respectively by the Zome du Mont Rose with its lustrous schists on one side, and by the Zome of Briancommais (Zome des Aiguilles d'Arves) and the Zome du Momt Blamc on the other. The last, or Sub-Alpime zone, is independent of this great fam. Its folds are variable, inclining most oftem toward the exterior of the Alps, but sometimes toward the interior. The great furrow traced by the Arly, the Isére, amd the Drac rivers seems to separate cleafly the Alpine massifs from the Sub-Alpine massifs in the mountainoys region which permits that classic division, though in reality this depression cuts obliquely a great mumber of folds. It is hardly possible to fix definite topographic delimitations for the several zones. Sculpture of the Groumd:- Alpine valleys are constituted by the association of trans- versal and longitudinal branches. Both consequent streams, following the shortest routes down the slopes, and subsequent streams, following the lines of the softer beds, are found in the Alps. The great depression traced by the Isere in its course from Albertville to Grenoble then the Drac, ows its existence to the non- resistant materials accumulated in the Alpine geosyncline during the Jurassic and Liassic periods. On the other hand, the valley of the Graisivaudan is independent of the direction of the folds which it cuts obliquely. The entrenchments of Grenoble and of Balme correspond to transversal sinkings of the architecture. Glaciation must also be taken into account in the study of Alpine sculpture. The glaciers of the Rhone, after having invaded the Swiss plain during the Pleistocene period, came against the Jura. Branches of this glacier extended westward taking advantage of the low peints in these mountains, especially in the direction of Natura, but the principal branch went toward the south encircling the crest of Grand-Colombier. On its path it also made contact with the glacier of the Arve, then, by the depression of the present lake of Bourget, with the glaciers of the Isere and the Arc and with the great Dauphinois glacier that spread over the valley of the Drac, of the Vénéon, and of the Romanche. This enormous mass of ice raised to a height of 1200 metres, encased by the sub-Alpine chains. To the north this glacier extended as far as Lyon where small glaciers are still found on the heights of Fourvieres, but to the south it did not leave the mountain zone to any great distaace, not extending even to Saint-Marcellin. The glaciers of the Durance, of the Var, and of the Tinde were more restrained due to a warmer southern climate. Erosion has removed most of the glacial deposits in this part of the Alps and rendered the reconstruction of these glacial domains difficult, but it is certain that they attained Saint-Martin-de-Vésubie. These Pleistocene glacial periods were separated by interglacial periods. The region of the Durance shows the effects of three separate periods of glaciation separated by periods of erosion. Geographic Divisions:- We shall study successively the masses of the Savoie, of the Dauphiné, of the Haute-Provence, and of the Comte de Nice, which include the Alpes Graies, the Alpes Cottienes, and the Maritime Alps (divisions of the Western Alps). Savoie: - The valley of the lsere and the valley of the Arly constitute a deep trough extending from Grenoble to Albertville, and separate two groups of mountain masses. On one side are the Sub=Alpine chains, on the other the Alpine chains. Sub-Alpine Part:~ To the north and west in the Sub-Alpine group the major architectural units are the Jura, the Depression of the Mollasse, the Sub-Alpine chains proper, and the PreAlpes du Chablais. Alpine Part:~ To the south and east of the Isere-Arly depres- sion we find the three Alpine zones: the Alpes du Mont Blanc, the Alpes de la Vanois, and the group of the Graisivaudan, le Maurienne, and la Romanche. Dauphine:- The great trough of the Graisivaudan is prolonged south of Grenoble by the valley of the Drac which winds in le Triéves and le Champ- saur travelling around the crystalline masses of the first Alpine zone. Its course follows the least resistant marly rocks of the Liassic and Middle Jurassic rather than any tectonic synclinal depression. The Alpine and Sub-Alpine zones of Dauphiné each have their own particular topographic characteristics. The first Alpine mass, after the Massif Central of Pelvoux, shows a considerable sinking of the axes of its folds. This si nking explains the local disappearance of the crystalline amygdaloidal masses which play such an important role in the petrography of §avoie. Hydrography of the Dauphineé:- It appears that the watercourses of the Durance system had acquired their positions at the end of the Miocene, without having deepened their valleys. At the end of the Pliocene epoch a large lake occupied the region extending southwest from Digne as far as Mirabeau. The Durance, the Bléomne, the Asse, and the Verdon emptied into this lake by their several channels, depositing their de- trital loads. This is the origin of the conglomerates that form the Plateau de Valensole, which joins the Alps proper to the Basse Provence. Haute-Provence; Comte de Nice:- The southern part of the Alps is divided inte the Alpes de la Haute-Provence to ‘the west of the Var, and the Maritime Alps to the east. Here the great depression of sculptural origin, which from Sallanches as far as Gap serves to separate the Alps into two major parts, disappears. This is due to the change from the marly character of the rocks to a more resistant facies, making slower the work of sculpture. It is almost im~ possible to differentiate the chain here into an Alpine and a Sub-Alpine chain; there is complete contact between the Alpine zome and the most exterior folds. A second important fact is that, while the most exterior mountains are arranged in paralled chains, the interior meuntains have an entirely different orographic arrangement, and seem to constitute indepen~ dent "paquets". The sculpture in this area is dependent upon the resistance of the rocks. Numerous inversions of relief are apparent in the Cret- aceous beds, like those of the Turonien, and in the Tertiary, like the Oligocene sandstone (called "le gres d'Annot"). This differential re- sistance to erosion explains the exotic arrangement of the interior mountain masses. The Alps of the Haute Provence present an uplifted appearance that is indicated by the Triassic heights at Remollon on the Durance, and by the carbonaceous sandstone ("grés houiller") at Barles. On the border are folds of an E.-W. orientation coming from the Sub-Alpine region, and Alpine folds of a N.-S. direction. In the Maritime Alps, studied particularly by M. Leon Bertrand, there are two anticlinal areas: that of the Mercantour and that of the Upper Var. The Mercantour area comprises an elliptical area of Crystalline rocks, the erosion of which has given rise to the sedimentary deposits which make the neighboring high valleys so fertile, in contrast with the arid calcareous valleys. As to the area of the upper Var, the dome of Barrot is its capital point; erosion here has exposed the strata only of Triassic and Permian age. Between these anticlinal areas are two synclinal areas, one situated to the north of the dome of Barrot, sometimes called the syn- clinal of the Sanguiniere, the other to the south including the synclines of the middle Var, of 1l'Esteron, of the Bevera, and of Menton. Inversions of relief appear in both these major synclinal areas making the original synclinal axes the present topographic eminences. Parallel mountain chains toward the exterior descend in the direction of Nice. BASSE-PROVENCE South of the Alps proper and bordering on the Mediterranean sea is the territory which we call the Basse~Provence. This territory presents two distinct natural elements, viz., the fragment of the ancient Tyrrhenide and the region of the provincial folds not affected by the Alpine movements. The first is represented by the mountains of the Maures and of 1'Esterel; the second by the mountains of the Basse-Provence, separated from the Alps by the Plateaux de raccord. Plateaux de raccord:- 2 Descending southward from the Alps we come into the "Zone des Barres", parallel chains cut by rivers descending toward the south and west. Next is the first of the Plateaux de raccord, namely the Plateau de Valens ole which is a moderately fertile territory composed of Tertiary rocks elevated by the last Alpine movements. This Tertiary plateau is succeeded by a suite of Jurassic plateaux of undulating surfaces largely denuded exposing the calcareous strata. Porosity of the rocks makes this region very arid. In all this region the Alpine influence is dominant; it is manifested by the orientation of certain valleys which follow the lines of the Alpine folding, and also by the inclination toward the south of the undulations and folds. : Mountains of the Basse-Provence:- The mountains of the Basse~Provence extend a short distance south of 8 line drawn from Grasse to the point of confluence of the Verdon with the Durance. All these heights, formed generally of cal- careous rocks, are 8rid and denuded or covered by only a meager forest growth. These mountains, though confused, seem to resemble the Alps in their oriented chains. Their structure is extremely complicated; ex- amples are found of complete overturning of the strata; the folds are often terminated abruptly at transversal depressions by peripheral faults. The valley of the Arc is important from point of view of the communication between France and Italy. This is a longitudinal element of relief, its position apparently of ancient date as it lies near the axis of the lagunes of the late Cretaceous and the lakes of the Eocene. Maures and Esterel:- South of the mountains of the Basse-Provence, and separated from them by the plain of Cuers and its valleys, is a fragment of the ancient Tyrrhenide cut by the lower valley of the Argems into two parts: les Maures and l'Esterel. Two factors control the architecture of this region; these are: the folds, now eroded, of the Hercynian epoch, and the uplifts of Tertiary date which rejuvenated the relief by a "“contre-coup" of the events which modeled the mountains of the Basse-Provence. VALLEY OF THE RHONE The valley of the Rhone constituted a great synclinal depres- sion (N.-S5.) as far as Vienne during the Hercynian epoch. After the dislocation of the Hercynian continent it was occupied by the Triassic lagoons and by seas during much of the Mesozoic time. At the end of the Cretaceous this valley emerged bit by bit. During the Eocene a continent- al valley existed here; during the Oligocene it was invaded by brakish lagoons. Marine invasions occured during the Miocene and again in the Pliocene, until this territory was given its continental character by the last movements of the Alpine revolution. Pleistocene glaciation was most active in the valley of the Rhone. The structure and sculpture show the effects of bhese successive periods of submergence, uplift, and erosion. CHAPTER FIVE - REGION TO THE SOUTH AND SOUTH WEST Historical Geologic Summary.- Major Divisions.- The event which gave to southern and south western France its geographic disposition was the formation of the Pyrenees. We shall review some of the events which preceeded the expression of this element of the Alpine folding. After the dislocation of the Hercynian continent, except at the debut of the Cretaceous period when there was a complete emersion, one uniform general situation persisted, with some variations, throughout all the Secondary (or Mesozoic) era. To the south of 1'Ilot central de la France there extended a large marine expanse, marked in the middle by another fragment of the Hercynian continent, la Meseta iberique. Between these two land afeas extended a third territory of elongated form in the approximate position of the Tyrrhenide. The Ilot central was terminated toward the south in a sort of peninsular form. After the general emersion occurring at the debut of the Tertiary era, a similar distribution of land and sea was established during a large part of the Eocene period. But soon the central land strip began to assert its importance; the zone of the Pyrenees folds were progressively elevated; the strait of Carcassonne was closed and gave to the sea of 1'Aquitaine the state of a gulf. The Oligocene and the Miocene saw this gulf reduced bit by bit giving place to lagoons. Thus entered the fluviatile regime to which the glacial phase of the Pleistocene reriod later brought its modifications. ; It is necessary to distinguish three major territorial elements in this region of southern and southwestern France. These are: the Pyrenees; the region of union between these mountains, le Massif central and la Provence, that is to say les Corbiéres, la Montagne Noire and le Languedoc; and finally 1l'Aquitaine. THE PYRENEES As in the case of the Alps, our ideas have been progressively modified concerning the architecture of the Pyrenees. Studies of these mountains have successivaly brought forth new theories and future work, especially on the Spanish territory, will undoubtedly lead us to new definite conclusions. The longitudinal disposition of the chain aad the almost axial position of the masses of primitive terrains and granites, make the Pyr- enees one of the regions best adapted to the theory of earth upheavel. Dufrenoy attributes the birth of these mountains to a special upheavel ("soulevement"), the upheavel of the Pyrenees, and assumes posterior or amterior movements to explain the presence of minor ranges which depart from the general direction of the chain, in particular the Corbiéres. Later, Magnan abandonned the idea of upheavel to prove that the relief was due to sinking of earth blocks provoked by the slow esontraction of the terrestial globe, and held that the Pyrenees derived their origin from numerous faults. But soon a number of detailed studies i the strata. showed the existence of energetic folds, even overturning The studies and personal works of MM. E. de Margerie and Schrader bi that this chain had a folded structure and was part of the Alpine £ Ye Since then the studies of the Pyrenees have progressed in a decisive fashion. a General Architecture:- Examination of a geologic map shows that the Pyrenees comprise two earth swellings or uplifts ("bombements") of unequal importance. These two uplifted areas are separated by a space of sunken folds. This ar position is responsible for the disappearance of the Primary terra sear the peak d'Orhy (in the western Pyrenees about 200 miles SE of Bayonne). These two uplifts are but the manifestation of the upheaving tendency which prevailed here throughout Mesozoic times in the axial part of the great marine depression between 1'Illot central de la France and la Meseta ibérique, and which connected these two land spaces during the Eoceme folding. : 5 In that part of the chain which extends from the liediterranean d'Or the el ted disposition of the ancient core and its I as Sy. of Bogan. ide and Tertiary terrains is most striking. This central zone is composed of great granite masses; the lateral zones are, on the French side the zones of 1'Ariége and the Petites Pyrenees, and on the Spanish side the zones of Mont-Perdu, of 1'iragon, and of the Sierras. The dips of the folds toward the exterior, that is toward the Miocene plains of the Ebre and the Garommne, indicate that the ensemble of these zones has the form of a composite fan. This fan is not symmetric, anal- ogous folds are not found on the two sides. In order to study the normal sequence of these zones, let us traverse the range from Toulouse toward Barbastro. After traversing the Miocene plain we come to the zone of the Petites Pyrenees composed of Upper Cretaceous and Eocene rocks with folds inclined toward the north. Next we pass into the Zone de 1l'Ariege, where the Lower Cretaceous and the Jurassié encircle island forms of Primary terrains and granitic cores. The Central Zone presents a vast expanse of Primary terrains marked here and there by granitic outcrops. Further south we pass into the Zone du Mont-Perdu, formed entirely of Upper Cretaceous and Eocene rocks with no exposures of granite; the folds here are frequently inclined toward the south. Soon the Cretaceous disappears beneath the Eocene; this is in the Zone de l'Aragon, the depressed architecture of which has permitted the maintainance of this relatively recent mantle. Last comes the Zone of the Sierras, the middle of which has been eroded down to the Cretaceous and even the Triassic rocks; the folds here resemble those of the Petites Pyrenees, but are infinitely more complex in plan. Sculpture of the Ground:- There ae the foot of the north slope of the Pyrenees, a belt of detrital terrains, of coarse elements, called the conglomerates of Palassou. On the southern slope, analagous materials cover the vast areas in the Zone de l'Aragon and in the plateaux which extend between the Sierras and the mountains de la Catalogne. These conglomerates are Eocene, but anterior to the close of that period; they have been uplifted by movements subsequent to their deposition. These particularities show clearly that an original important relief was uplifted before the close of the Eocene, and that it had been subjected to considerable erosion before the last orogenic movements gave to this chain its definite architecture. They also prove that, in that first phase of sculpture, the atmospheric conditions were essentially the same on the two sides. Since this first phase of erosional attack, however, the work of reduction has proceeded much faster on the northern slope, where the Tertiary formations have been almost entirely removed and many of the Secondary beds have disappeared. On the southern slope, much of the Eocene strata still remains, This difference in the rate of erosion is due to the sheltered position of the sm uthern slope as compared with the exposure of the northern slope to the humid and violent winds coming from the Atlantic. Glaciation was also more intense on the French side of the Pyrenees. : Entering the intertor of this chain we observe a convexity of the line of the mountain mass toward the south due to the factors which have favored erosion on the French side. The hydrographic system of the Nive has cut down to the ancient rock core; some of the high summits, like le Marbord, are of Cretaceous rocks; the Mont Perdu is covered with a mantle of Ebcene. The watercourses on the southern flanks of the Pyrenees conform largely to the structural lines; on the north the valleys are sculptural, the streams conforming only in a few local instances to the tectonic structure. CORBIERES - MONTAGNE NOIRE ~- LANGUEDOC - Corbieres:- The Corbieres are a mountain mass of the Pyrenean chain, border- ing on the Mediterranean to the east, and lying in general between the channels of the lower Aude and Agly rivers. Geologic history shows us that, during Secondary times, a sort of isthmus joined the Ilot Central with the core of the future chain of Pyrenees. At that time the area of the present Corbidres was occupied by a number of islets. At the end of the Eocene period the region was folded and given its continental form. The Corbieres may be divided into the UBF 18Brbieres ("Hautes Corbieres") and the Northern Corbieres. The former correspond to the exposures of ancient terrains, the group of which is also called the Massif de Mouthoumet. Their western extremity, situated near Durban, forms a veritable headlands against which the folds of the Pyrenees adjut. In all these mountains the folding becomes more intense as the Pyrenees are approached, the folds inclining toward the north. The marly char- acter of the rocks makes the region barren and desolate. The upper course of the Aude flows in a transversal depression of the folds. The Algy takes its course without utilizing the important synclinal valley of Saint-Paul-de-Fenouillet, and cuts in profound gorges the anticline of Lesquerde and the crystalline terrains to the south. This stream is probably was probably determined by the ancient structural sur- face, being later superimposed upon the present topography. Montagne Noire:- The Montagne Noire is that emsemble of heights formed of ancient terrains that extends from the depression of Carcassonne to Causses, form- ing a facade on le Bas-Languedoc, and Joining to the north with the L crystalline plateaux of Rouergue. They form the farthest point of advance of the Massif Central of France. These heights offer to our eyes a frag- | ment of ancient Hercynian France, rejuvenated in a certian measure during the Tertiary period. | After having rested in an emerged state during the Secondary era, the territory of the Montagne Noire, at the time of the formation of the Pyrenees, acted as a buttress by reason of its rigidity and exerted its force upon the areas to the south. These movements of Tertiary date had some influence upon the present topography, but most of the relief forms are due to the particular- ities of the ancient uplifted peneplain and the Hercynian structure. This antique architecture comprised a core of metamorphic gneiss rocks bordered by bands of Primary terrains. This Primary border disappears to the west under the Tertiary sediments of Castrais and Lauraguais; its northern part constitutes the Monts de lacaune, and its southern part the Mountains of Minervois, sep- arated from the gneissic mass, which rises 300 to 400 metres above it, by the valley of the Jaur. The coal basin of Graissessac is located to the | northeast. The Montagne Noire is joined to the Massif Central by the monotonous plateaux of Rouergue on the north. To the east are found its highest poihts - Levezou and the Montagne des Palanges. Bas-Languedoc: - The Bas-Languedoc extends from the Montagne Noire to the sea. It is a folded zone, prolonging the Pyrenees chains which extend around the Corbieres, but where the folds are often buried by later sediments. In this region we distinguish two groups of folds separated by a trough-like zone which corresponds to the lower courses of the Orb and the Herault. The western group comprises the folds of the Montagne de la Clape and those of Saint-Chinian, where Cretaceous and Jurassic- Triassic rocks appear respectively. The eastern group is subdivided into three folds separated by synclinal depressions; these folds are the folds of Gardiole, of Montpellier, andi of the peak of Saint-Loup, where Lower Liassic, Middle Liassic, and Middle Jurassic rocks appear respectively. AQUITAINE We shall consider as a part of the /Aguitaine all the country that extends between the ancient rocks of Vendee, of the Massif Central, and of the Montagne Noire on one side, and the Pyrenees on the other. This region has the form of a geographic basin, all the waters of the Ardour and the Charente emptying into the sea through a single estuary. The Aquitaine may be divided into several regions of different characteristics. These are: (1) the Northern region, where from north to south, in a more or less regular fashion, the Jurassic, the Cretaceous, and the Tertiary beds appear; (2) the Eastern Region, where only the Tertiary appears dipping toward the ancient terrains of Rouergue and the Montagne Noire; (3) the Sub-Pyrenean region, where the Tertiary deposits are largely covered Quaternary materials of fluvio-glacial origin; (4) the Plateau Landais, where the Pleistocene gravels obscure the older formations. Aeolian deposits also characterize the Plateau Landais. CHAPTER SIX - REGION T0 THE WEST Major Divisions:- From the moment of the dislocation of the Hercynian contin- ent, the West of France showed a particular resistance for which the lagoons and the seas of the Permian and Triassic seemed to show respect. During all the Secondary era this region, almost in its totality, con- stituted an integral part of a continent which was prolonged toward the Atlantic as far as English Cornwall, and joined at different times the Ilot Central of France. It was not until the Tertiary era that this situation was changed, when, with the general emersion, this island area of the West of France was joined, in peninsula form of varying outlines, to the continent of Europe. The outstanding fact brought out by this geologic history is that since Hercynian times up to the present, apart from a partial Miocene invasion and a brief submergence during the Pliocene epoch, a large part of the region to the West has escaped all marine invasions and has been exposed to the destructive action of exterior agents. Moreover, the Post-Hercynian orogenic movements have operated but little in this region; as a result we see today, in great expanse and almost without modifications, the peneplain due to the erosion of the ancient Hercynian relief. It is necessary to distinguish with care the part where that peneplain is visible, from the areas where it is masked by the Secondary or Tertiary deposits. We shall therefore study separately the "Massif Armoricain" and its Marginal Regions. MASSIF ARMORICAIN General Considerations:- The deep cut of the Gulf of Saint Malo and the channel of the Loire intorduce, in the geographic description of the Massif Armor- icain, three divisions which we must distinguish successively, viz., Brittany, Cotentin, and Vendée. In these three areas the topography is a reflex consequence of the ancient Hercynian architecture. The differences in resistance of the materials of the soil have given in many places an inversion of relief. ; The Amoricain region was energetically folded during the Carboniferous period, forming folds with a general E.-W. direction. M. Ch. Barrois has shown that this Carboniferous folding consisted of two phases in which the directions of the folding were sensibly different. All the architecture that we see today is eroded to a great degree. Igneous intrusions are seen in many places; often we find representatives of a complete series of Primary sediments in the tec- tonic depressions. Brittany:- M. Ch.Barrois has shown that the Carboniferous folds of Brittany are grouped so as to form a large synclinal zone between two anticlinal bands. One of these latter, the anticline of Cornwall, appears to have been formed at the time of the most remote folding; it extends from the Isle of Sein to Nantes. The other, the anticline of Leon, is directed from Brest to Guernesey. Both of these anticlines bring to light the most ancient rocks, which have been called the fundamental gneisses. The syncline between has a gmeral easterly trend. The basins of Chateaulin, Laval, and Belair exist as tec- tonic depressions in this area. Granites of many different periods have intruded Brittany, the most recent being in tue Carboniferous anticiines. M. Ch.Barrois has proposed the following topographic sub- division of Brittamy: lst tne Northern Plateau, including the plateaux of Léon, of Tregorois, of Penthiévre, and of Poudouvre; 2nd the South- em Plateau, comprising the plateau of Cornwall, and the plateau of Bain; ord the Axial Region, having for subdivisions the Bassins of Chateaulin and of laval, and the Plateau of Rohan. The topographic relief of Brittany varies between 100 and 300 metres; it cam therefore hardly be qualified as being either a flat or & mountainous region. Certain eminences rise above the general level where the rocks, such as certain granites& Silurian sandstones (called gres Armoricains) which have been converted to quartzites by metamorphic action, are of a superior resistance to erosion. This is the origin of the Montagne d'Arree, a granitic mass with flanks of metamorphosed sed- iments. Likewise the quartzite at Menez Hom, of the Montagne Noire, of Coévrons, and of the Forest of Ecouves. In the Southern Plateau the anticline of Gormwall plays an important role. The undulations expose alternately bands 6f granites and of cristallophyllien terrains, gneiss to the west, mica schists to the east. In the Northern Plateau, the great anticlinal which is the homologue of the anticline of Cornwall forms the Pays de Léon. The soil here is fertile thanks to the abundant humidity, and in the Trégorois, to the presence of ancient decomposed eruptive materials and to a mantle of Quaternary alluvium. Diabase occurs in le Penthidvre and the Plateau de Poudouvre. Toward the west, the Bassin of Chateaulin, formed of Devonian and Carboniferous terrains of argillaceous schist, presents a prairie land which contrasts with the bordering areas of the Montagne d'Arree and the Montagnes Noires. To the east, the Bassin de Laval occupies a position sym- metric with that of Chateaulin; it is composed of Devonian and Carbonif- erous terrains of a calcareous nature, a good agricultural land. Finally, the Plateau de Rohan in the center serves as a sort of transitional territory between the Southern Plateau and the Bassins of Chateaulin and Laval. It is constituted of Cambrian formations, called the phyllades de Saint-Lo. This is pasture land for the most part with the exception of a few forest areas. The western part is of a relative fertility due to the presence of some Tertiary deposits and to a mantle of alluvium. Cotentin:~ To the north of Brittany is Cotentin, a high lying area with ridges elongated in a general E.-W. direction. A large part of the relief is granitic, the rest chiefly metamorphosed Silurian sandstones. Tertiary deposits in the low zone of the lands of Lessay indicate that the northern part of Cotentin existed as an island during the Miocene epoch. Tendo: ~ la Vendee is separated from Brittany by the lower course of the { Loire. The depressed structural situation of this earth block seems to reflect the condition in past ages. Deposits of Tertiary terrains of diverse ages, as well as those of Cretaceous date show that since Her- cynian timew the sea has invaded this area upon many occasions. Near Chantormay., a longitudinal fault has exposed the fragment of a coal deposit and a few patches of Jurassic limestones. The influence of the ancient Hercynian architecture is seen in the course of the Loire, which follows the direction of the folds in a part of the basin of Ancenis and in its journey from Nantes to Paimboef. MARGINAL REGIONS The countries which form the margin of the Massif Armoricain are part of the Parisian Region, though these areas have quite a different topography and geologic history from the Region to the North East of France. Normandie is that territory which extends between the Massif Armoricain, the shore line, the lower Seine, and the Merlerault. Here the structural undulations have only a minor effect upon the topography, the dominant factor being the general dip of the strata toward the N.E. Travelling from west to east one encounters successively younger beds; first the Jurassic, then the Cretaceous, and finally a siliceous (flint) to argillaceous mantle, resulting probably from the modification in place, during the Eocene period, of the deposits overlying the chalk. The Jurassic part of Normandie includes: le Bessin pasturages of argillaceous Liassic beds, and la Campagne de Caen, an agricultural territory of Middle Jurassic strata. The Cretaceous appears in the Pays d'Auge (chert and clay) and in the Roumois and the Campagne de Neubourg (chalk). This Cretaceous chalk disappears under the clay mantle in le Thimerais, la Plaine de Saint-Andre, 1'Ouche, and les Terres francaises which derive their agricultural value from a covering of alluvium. In the middle of these marginal territories is le Perche and le Bas Maine. Here the topography is influenced largely by a group of faults having a general E.-W. orientation. The Jurassic area of le Perche comprises la campagne d'Alencon, le Saosnois, and la Campagne de Conlie - fertile agricultural land. The Cretaceous areas are chiefly pasturages. In the middle of these, little Jurassic islets appear, due to the in- fluence of faulting. Le Poitou is a relatively depressed area between la Vendée and 1'Ilot central; this territory existed as a strait playing a part similar to that of the Morvanno-Vosgien strait in former geologic ages. Sedimentary rocks of Eocene and Oligocene age are the most important beds exposed. Anticlinal folds in this region have a general N.W.-S.E. direction, influencing in a certain measure the courses of the rivers. The lands bordering on the Loire are also relatively de- pressed. Here we find traces of a Cretaceous transgression and of a marine invasion of Miocene date which deposited shell-marls (faluns') as far as Blois. Eocene and Oligocene fresh water deposits also occur. Hydrography: - The hydrography of this Region to the West of France is subject to a number of diverse influences which predominate in their turn. The See and the Sélune, which border the Avranchin fold, take their courses as a result of the structure of the ancient Hercynian base. . The lower course of the Seine conforms with architectural influences of Tertiary date. In particular, the course of the Eure follows suc- cessively three synclinal undulations. The upper courses of the Mayenns, the Sarthe, and the Huisne pursue the lines of depressed blocks. A last remark is important regarding the hypsometry of Western France. The relative uplift of the land which brought about the retreat of the Miocene seas instituted a new cycle of erosion. The antique peneplain, entered upon this new cycle of sculpture, had its watercourses profoundly entrenched. In a number of streams, small - cascades indicate that the resistances of the rock materials hawe not yet been overcome, and many of the rivers, though old from one point of view have the characteristics of youth. * % *% * CHAPTER SEVEN - CENTRAL REGION OF FRANCE General Cons iderations:- The vast expanse oecupied by the anciemt terrains in cemtral France has long attracted the attention of geologists by reason of the contrasts which it presents with the bordering regions where only the most recent formations appear. The general history of Europe and of France shows us that in the most remote periods of the history of the earth, an emerged territory existed in the region which today forms the center of France. We know that this llot Central, after having served as a basis for sedimentation in the middle of the Primary seas, was included in the general mass of the Hercynian continent with its neighbors and affected by the folding of that epoch. We also know that at the time the Hercynian continent, worn to the state of a peneplain, was definitely dislocated, the central part of France returned to the insular condition, and that a new Ilot Central subsisted in the heart of the Secondary seas which encroached more or less upon its surface. Finally we know that the Tertiary phase of emergence united this isle with the continental ensemble; this is the present situation. : This Central Region now offers to our eyes a part of the ancient Hercynian peneplain surrounded on all its margins by Mesozoic or Tertiary beds. It was once thought that the nappe of ancient terrains which we see today emerged bit by bit in a fairly regular fashion, and that the limits of the Secondary terrains represented the successive stages of retreat of the seas. We now know that these present limits have no historic value, and that many parts of the Central Region were covered with a Mesozoic mantle now disappeared. It is necessary to consider a cause for this decapitation. M. Suess advanced the theory of a horst and held that the immobility of this region sufficed to explain its exposures of ancient strata under a new cycle of erosion. This immobility is now believed to be a fiction, also that this mass of ancient terrains has not only been affected by re-elevations, but by appreciable deform- ations. The only difference between this area and others affected by the Alpine movements is that the rigidity of the ancient terrains has caused them to be broken into blocks, rather than folded, and in certain places these breaks have served as avenues for the extrusion of eruptive materials. After the dislocation of the Hercynian continent many com- plex events have contributed to the determination of the present geo- graphic forms in this Central Region of France. The movements of the Secondary era are not well known. The Ilot Central appears to have been at its minimum during the Middle Jur- assic epoch. At the end of the Jurassic and during the Lower Cretaceous, however, the marine waters had receeded frem this entire region. All the displacements of the base level were not accomplished by simple uplifts and subsidences of the Central Region; many warpings of the crust had their effect upon the architectural modifications. The architectural modifications of the Tertiary era are most important as they have determined the major divisions of the present relief. There appear to have been two separate orogenic phases affecting this area during the Tertiary, namely the Pyrenean and the Alpine phase. The movements in this area contemporaneous with the Alpine Revolution were the more important. The relief, vague and poorly out- lined at the end of the Oligocene, was uplifted sharply during the Mioceme. Large fluviatile courses were established which deposited vast detrital deposits over the Parisian region. These Alpine undulations took the form of faults in some regions, and thus determined the longitudinal depressions of the Loire and the Allier. Under the effect df these dis- locations, the larger part of which were accomplished before the end of the Mioceme period but which continued to some extent into the Pleistocene, many eruptive materials were extruded. The elevated rock base, thus broken and partly covered by volcanic material, entered into a new cycle of sculpture. The present topographic forms were gradually designed under the influence of the Alpine movements as well as the ancient Primary architecture in the exhumed parts of the Hercynian base. Coal deposits are found in this Central Region, not in the form of a stratum of wide extent as in the Franco-Belgian region, but as little isolated basins, probably remnants of deposits once much more extensive. These deposits give some indication of the Hercynian arch- itecture; those of le Morvan, of Saint-Etienne, and of Blanzy to the east follow the direction of the folding, while those in the central part from Champagnac to St.Eloi line up with the great faults of Mauriac and d'Argentat. The Tertiary materials may be grouped into three classes: the sediments, the eruptive materials, and the glacial detritus. Of these the sediments were at one time the most extensive, but have largely dis- appeared under the effects of erosion, being conserved in certain places only due to accidental causes - a relative sinking of the earth or the superposition of a protecting eruptive layer. Most of the eruptive materials are of Pliocene date, some of Miocene age. The most condiderable extrusions are those at L'Aubrac, le Cantal, 1'Auvergne, Mont Dore and Monts Dome; these areas are west of Lyon neighboring the headwaters of the Allier. A wide variety of eruptive materials is to be found in these areas. Tuffs and cinters alternate with lavas (basalts, trachytes, dolomites, andesites, and phonolites.) None of these materials seems to be characteristic of any one epoch or of any one locality. The topographic forms resulting from the sculpture of these: igneous rocks are also widely varied; here we find small lava plains, there protruding dikes and buttes as the result of injections. Evidences of two distince glacial periods, separated by a long erosional interval, are found in the Central Region. The first of these occurred in the Pliocene, and covered considerable area in the vicinity of Cézallier, of Cantal, and of Mont Dore, its accumulations of detritus extending as far as the plateaux which dominate the right (east) banks of the Dordogne. The second glacial period was in the Pleistocene; the glaciers then were localized in the valleys, in the manner of the Alpine glaciers of today. Their frontal and lateral morraines are found in nearly all the valleys of Cantal. Major Divisions of the Massif ancien:- It is the recent architectural modifications which have given this area its major geographic divisions. The valleys of the Loire and the Allier establish divisions of a general N.~S. direction. Going from east to west we encounter first the "Escarpe orien- tale" (or eastern escarpment) forming a facade over the valley of the Rhone; this establishes the separation between the slope of the Atlantic and that toward the Mediterranean. The two other divisions, known res- pectively as the Monts du Forez and du Velay and the Monts d'Auvergne, border the upper valleys of the Loire and the Allier. These reliefs correspond to the outlines of the Alpine undulations; numerous faults, parallel to their general direction, break them into more or less sunken bldcks. In their southern parts, these areas grade into the plateaux of Grevaudan. astern Escarpment:- The heights which terminate the lassif central on its eastern border rise abruptly above the great depression traced by the valleys of the Saone and the Rhone. Relatively low and broken to the north, where thy separate the valley of the Saone from that of the Loire, they become higher and more important as one descends toward the south, taking finally, in le Vivarais and les Cévennes, an absolutely massive character. The differences in the nature of this mountain mass throughout is due to a number of causes: in the first place, the Alpine readjustment has not affected the entire area in the same manner; in certain places the ancient Hercynian peneplain has escaped the Mesozoic seas; elsewhere it has been completely covered by a sedimentary mantle; finally, that peneplain presents a certain diversity in the nature of its materials and in their tectonic arrangement. In the northern section, between the Dheune and the Gier, the influence of the Alpine movements has been most considerable. Here we find bands of Secondary terrains alternating with parts of the ancient peneplain exhumed by erosion, and introducing radical changes in the topographic forms and in the vegetation. Moreover, the ancient peneplain has a very complex architecture. M.Michel Levy has shown the existence of a system of faults or fractures of a N.W. direction superimposed upon Primary folds of a N.E, orientation. Thus we find some valleys conform- ing to the Hercynian folds, as in the valley of the Dheune, the valleys of the Arconce, and of the Brévemme, while other topographic features show a N.~S5. orientation. To the north, the Monts du Chardlais and the Monts du Maconnais dominate reppectively the plains of the Loire and the Saone. Tertiary, Jurassic, and Triassic rocks are exposed in this region as well as the ancient strata. In the southern part we find the basaltic plateaux (eruptions of Miocene date) of the Mts. des Coiroms, and the Jurassic rocks of les Causses. The watercourses here have largely developed in conformity to the Jurassic architecture. Western Part of the Massif ancien:- The great line of coal deposits which runs diagonally to the west of the Monts d'Auvergne, in the neighborhood of the fault of Mauriac, marks the beginning of the western part of the Massif central. This territory to the west consists almost entirely of ancient rocks; in its northern part are the Monts de la Marche; to the south the Monts du Limousin; to the east are the plateau of Millevaches, le Franc Alleud, and la Combrailles. The drainage lines of the western part of the Massif central have been influenced by the two depressions of 1l'Aguitaine and of the Loire, and have been gradually entrenched in the ancient peneplain. Borders of the Massif ancien:- We define the margins of the Massif ancien as those expanses of Secondary and Tertiary terrains, situated around its border, which have not been removed by erosion. To the east we find the Secondary rocks in the regions of Maconnais, of Chalomnais, of Lyonnais, and of Vivarais. To the south the nappes of the Causses terminate the Hercynian base. To the south-west, the undulations of l'Aquitaine resolve themselves into faults at the limit of the Massif ancien. It remains for us to examine the northern border where the Massif ancien makes contact with the Parisian Region. To the north, in the territory between the Massif ancien and the middle Loire, we find Tertiary terrains deposited upon a Secondary mantle, and showing an alternation of detrital deposits with lacustrine. With erosional sculpture this condition has given rise te the development of terraces and cornices, though not as distinct or continuous as in the western Parisian region. : During the uplift of the Massif Central, two series of tec- tonic movements influenced this northern border. The first was that of the N.~S. faulting which has broken the area of le Nivernais and le Sancerrois; the second was the undulations of the Parisian region. The influence of these movements upon the design of certain topographic traits is very apparent. The N.-S. faults have determined the position of the valley of the Loire as far as Briare, accompanied by a tilting of the land toward the west. The undulations have localized the course of the Indre, and that of the Loire from Gien to Orléans. The Secondary mantle in this northern border region is cover- ed in many places with a Tertiary layer, the elements of which are either of detrital or calcareous nature. La Bremne and la Sologne are regions of sands and clays, occupied by woods, moors, and ponds. In la Champagne Berrichomme, Tertiary lacustral, calcarious beds alternate with exposures of the Jurassic platform. In the valley of Orléans, alluviums brought in by the Loire create a band of country whose fertility contrasts with the aridity of la Sologne. CHAPTER EIGHT - THE SEA COASTS Origin of the Shore Lines:- Before any detailed study, it will be well to inquire into the cimcumstances which have fixed the present coast lines of France. The question arises: What sections have a more fundamental character than the others, that is which coast lines have been most stable throughout the varying events of geologic time? The hypothetical map below shows the effect of a relative displacement of 100 metres in the level of the seas. We see that the coast in the Mediterranean Region is most fundamental; also that France Present Shore Lineg and Hypothetical Shore Lines of France Assuming Regpectivel o Rise and a Fall of 100 meters in the Level of dhe os (From “L' Architecture du Sel de la Fronce ) rests upon a part of the same base that supports the British Isles, and on which the sea intrudes in simple depressions to form the English Channel and the North Sea. We naturally then make the distinction between ghallow seas and deep seas; the English Channel and the North Sea of teday are undoubtedly comparable to the waters which omncé advan- ced into the Parisian Region, and the situation of Corsica and Sicily presents an analogy with certain ancient islets, like Mercantour, which existed in the middle of the Alpine seas. In the Mediterranean region, the principal tectonic event has been the dislocation of the Tyrrhenide; in the Oceanic region it » has been the destruction of the North Atlantic Continemt. These are the earth subsidences which have determined the gemeral layout, the new positions of the continental platform and the abyssmal seas. As to the shore lines, regulated by the transgression more or less con- siderable of the waters on the continental platform, these have been designed under the effect of secondary causes. It is necessary to make some distinction as regards these secondary couses. Ome type is of the tectonic order, corresponding to minor movements which accompany or follow the major tectonic movements. The other causes are sculptural, for example, sapping action by the waves, the heaping up of alluviums, the advancement of deltas, the formation of littoral deposits, etc. SHORE LINES OF THE MEDITERRANEAN The Mediterranean sea was reduced to its minimum domain after the Alpine Revolution at the end of the Miocene period. Arms of the sea which formerly extended as far as the Alps by way of the valley of the Rhone disappeared. During the Pliocene period the land again subsided and admitted the sea as far ad Lyon in the Rhone valley, designing also the gulfs of Genoa and of Lion. Relative uplift occur- red in the Quaternary era giving the coast its approximate present contour, to be modified only by certain erosional and sculpturing processes. : Gulf of Genoa and Gulf of Lion:- In comparing the general trace of the coast line with the disposition of the continental platform designed by the bathymetric lines, we find a fundamental difference in the constitution of the gulf of Genoa from that of the gulf of Lion. The former has what we have called a fundamental character. The second is but an encroachment of the sea upon the continental platform, and is therefore easily subject to considerable change in its outlines and dimensions. The gulf of Genoa was directly formed by the post-Alpine movements. These movements also greatly enlarged the gulf of Lion, the sea advancing as far as Viemna. The unstable character of the valley of the Rhone has facilitated the encroachment of the Mediterranean in this area throughbtut geologic time. : These two great gulfs, separated by an inverse curve con- stituting the Provence, fomthe Mediterranean coast line of France. Shore Lines of la Provence:- The shores of Provence correspond to three geographic el- ements whose characters we have already studied; these are: the Alps, the ancient massifs of Maures and of Esterel, and the mountains of the Basse Provence. The Alpine section presents a suite of small indentations, among which that at Villefranche is the most considerable. The border- ing heights, the Mont Boron and the Cap Ferrat, have a disposition roughly perpendicular to the general direction of the coast line, and indicate a suite of folds cut by the normal of the continental platform. To the west of Nice, the mouth of the Var forms a land height due to the accummlation of alluviums. These alluviums rest upon a Pliocene terrain, the upper beds of which indicate the presence of an ancient marine delta. The valley of the Var once formed a deep cut whose disappearance is due not only to alluviation, but also to general uplift of the land. Beyond the Var, we find Jurassic and Triassic terrains whose folds form a crescent shape. In the coast of the Maures, the existence of the Gulf of Grimaud and the presence of the base that supports the isles of Hyeres, the rocky extremity of the peninsula of Giens and that of Cape Sicie are explained by the Tertiary dislocations and the succession of anticlinal and synclinal zones. Littoral deposits have smoothed out the coast line in this region, and have connected to the continent the ancient isles of Giens and of the cape of Cépet. This work has been done in the present era, and no Pliocene sediments are found here analagous to those of the district of Nice and Ligurie. The peninsula of Cape Sicié, limited to the north by the bay of Saint Nazaire, marks the apparent end of the chain of the Maures, their mass being prolonged, however, bems&ith the Mediterranean waters, con- stituting part of the continental platform. Delta of the Rhone:- The delta of the Rhone is of recent date and has been formed by the progressive piling up of alluviums, building up the estuary of the Rhone. This process has been favored by the absence of tides, and by the gentleness of the slope of the submerged platform. The disposition of the surrounding dittoral deposits here, indicates a great stability of tne shore line tmroughout mauy ages. Coasts of the languedoc and of the Roussillon:- The same action of the littoral deposits whicn has facilitated tue building up of tne estuary of tne Rhone and the formation of its delta, has regulated the shore lines of Languedoc. The materials carried along tiie coast under the influence of currents and winds have found a certain number of protected places of deposition, and have thus transformed the primitive irregularities of the shoreline into lagoons whicn no longer connect witn tune sea. : The plain of Roussillon has a tectonic origin, a veritable gap formed by a sinking in the Pyrenean mass. There tne Pliocene sea advanced in a large gulf, its ramifications extending into the mountain mass. There first were accumulated marine deposits of delta cnaracter, then, aiter an uplift of the land, fresh water deposits. Today, that level coast is bordered by a dittoral cordon, whicn has found its pretect- ing points in the Cape of Leucate and the rocky projections above tae Cape Béar. The mouths of the Tech and of tue Tet design slignt entrants dn its regular curve. The ancient lagoons are already almost completely filled in. Soutn of tue plain of Roussillon, tne coast becomes rocky approacning nearer to tne border of tne continental platforu. Lorsica:- The disposition of the bathymetric lines show the geographic aependance of Corsica witn Italy. The common base, which supports this isle and that of Safdinia, is prolonged toward tne Italian coast under | ! / marine depths of not more than 200 meters. Numerous islets indicate the line of union. On the other hand abysmal depths of some 3000 meters Separate this isle from tne French coast. We have evidence, however, of an ancient connection witn the Pyrenean core and with tne Maures. Corsica is not a tectonic unit; it is formed of two distinct parts: a folded band of Alpine character, and a fragment of the ancient Tyrrhenide, tne Cot Corsten relief of which has been rejuvenated by subsequent dislocations. The accom panying geologic map illustrates these divisions. ec) To the S.W. the g §) | 9Bastia rocks are almost entirely ; of ancient date, chief- ly granitic. To the N.E. after a discontinuous band of Eocene deposits, we find schistose ter- rains, the age of which Gulf is uncertain. These ae vorto beds are energetically : folded and traversed by recent eruptives analog- ous to those of the Alps. To the S.W. faulting has played the most important LEGEND role. = The somet- os ry of this isle Rpsue Hiayian Tagen two regions of distinct architecture separated by Alpine Region a large diagonal trough a pas about ten kilometers in © KF £2 Tertiary width. As M. Nentien ob- ~~ ./ serves, if Corsica were : A Quaternary to sink down 600 meters, it would be cut in two by an arm of the sea; this Georocic Map or CorsiCA is reminiscent of the dis- _ -—— position during tne Eocene epoch. In Alpine Corsica, the N.-S. direction of the topographic features is due to an anzlogous orientation of the folds. This is also tne explanation for the existence of tne peminsula of Cape Corsica. In Hercymian Corsica, where all tne valleys are oriented S.W.-N.E. and form compartments isolated from each other by important mountain chains of the same general direction, it is tue Hercynian architecture which dominates. Rejuvenation of this relief has brought the erosiomal forces into play. The east coast of Corsica is fairly level, with the shoreline paralleling the direction of the folds; this produces an even coast line. The west coast, on the other hand, is very irregular, cutting transversally tue tectonic axes. Mountains adjut directly on the sea, and great gulfs mark the relatively sunken parts of the Hercynian base. At Bonifacto we find vertical cliffs of sa calcareous Mioc FR yeriical oii ndy éne rocks, formed by sapping fi THE ATLANTIC SEA COASTS Origin of the Continental Platform: ~- The works of M. Suess and Neumayr show that, during Secondary times, the part of the globe which at present constitutes the north of tine Atlantic was occupied by a vast continent of which Canada and & large part of Northern Europe are but tne remmants. To tne soutn of this Nortin-Atlan- tic Continent extended a sea which was prolonged as far as tne heart of Asia. That sea, of whicn the Mediterranean troughs constituted but a small parc, encroached more or less upon the continent, following movements of the terrestrial crust, or accessory phenomena like the deposition of sediments or a cnange in base level. M. Suess has given it the name TETHYS. This situation was continued during the greatest part of the Tertiary era, with certain displacements of the shore lines due to marine transgressions or regressions. During tune Eocene period, communication was made between tne Atlantic and Mediterranean parts of Tethys by the Betique Strait and the Gulf of Gascony. There sediments were accumulated in th¢ geosynclinal troughs waich were soon to form the folded chains of the Betique Cordillera and tne Pyrenees. Certain gulfs advanced into tne interior of the land, notably on tne lower Loire and on the axis of tne English Channel. The uplift of tne Pyrenees folds, joining the ancient core of the Pyrenees to tne massif of Mouthoumet and to the Montagne Noire, trans- formed l'Aquitaine into a closed gulf. During tne Miocene period tue sea invaded as far as the region of Blois, forming shell marl deposits. At tne end of tne Pliocene period came a radical change, tne sinking of tune Norton Atlantic Continent. To that epoch dates tne form- ation of tne present continental platform. Zhe Gulf of Gascony and the British Channel:- The lines of the Gulf of Gascony are but the result of over- flowing of the sea upon the continental platform determined by the sub~ sidences of late Tertiary times. The submarine topography here points to this conclusion. To tne soutu, the line of the Pyrenees, a rocky plateau shorn of its sediments by the winds, shows a very complicated disposition extending as far as Cape Breton. To tne north, tne islands off tne Armoricain coast represent tne most elevated parts of a relief invaded by the marine waters. In the center, the sands of Landes present an aeolian plain. The Irish Sea, the English Channel and the North Sea represent simple encroachments of the Atlantic upon the European base. | The English Channel, in particular, is tne result of very | recent modifications. Fluctuations of la Tethys continued during the | Pleistocene period. At a certain time, that which is today the British Channel amd tne North Sea were completely emerged; the mouth of tie Rhine was located in the neighborhood of Norway, and the Seine, uniting its waters to tne Somme, reached the ocean by a synclinal depression corres- ponding to the present axis of the English Channel. A last relative depression of tne continental base permitted the sea to invade this area; but for a long period of time, even wp to the beginning of historic times, an isthmus connected France with England at the point of the present Straight of Calais. Its disappearance may be attributed to the sculpture 0f the ground and to the sapping action of the waves, thus fashioning the dy Channel. The coasts of France and of England indicate that tectonic movements of subsidence have deepened the English Channel since the dawn of tne historic period. Coasts of l'Aquitaine:- The shores of l'Aquitaine are outlined by the Gulf of Gascony. They arise by a rocky section where the sea bathes the mountainous fronts of the Pays Basque, and form embayments in tne valleys of the Bidassoa and the Nivelle. The continental relief is continued by a submarine topog- raphy of unstable character, whicu is uplifted in the rocky plateaux of Saint Jean de Luz (off tne coast of Biarritz), and sunken in tne proloug- ations of tne terrestrial valleys. It appears, from the presence of cer- tain rocks and snoals visible from the shore, that the architecture of the Pays Basque is prolonged into the oceanic domain. Near Biarritz commence tne shores of Landes, whose relief is marked by the presence of a number of dunes, some rising to a height of around 70 metres. Numerous small ponds in this region are due to the accumulation of fresh waters brought in by small streams into basins formed by surrounding dunes. The basin d'Arcachon is an exception, not only because of the importance of the river which empties into it, the Leyre, but because the marine waters have here penetrated a breach in the barrier of dunes. . The Isle d'Oléron corresponds to an anticlinal undulation rising out of tne sea, the southern prolongation of which undoubtedly appears in the rocky submarine plateaux of Rochebomme. The Pertuis d'Ant- iocne, tne Isle of Re, and tae Pertuis (defile or gap) Breton represent dislocations of the northern flank of that anticline. This section of the coast line throughout shows modifications which are evidence of recent emergence. Coasts of 1'Armorique:- The shores of 1'Armorique, la Vendée, Brittany, and le Cotentin belong almost equally to tne Atlantic Ocean and to tne English Chammel. The nature of tne diverse ancient rocks here and their alternation under the eifect of the folded Hercynian architecture has given certain general characters to their ensemble. The spur form which the European base pre-~ sents at this place has progressively receeded under the attack of the waves. Subsidence of tnis land has had an equally important role. The coast bordering tue Atlantic describes a regular curve continuous with tmat of tne Gulf of Gascony but marked by innumerable irregularities of varied form. A numoer of small islands exist a short distance out, roughly parallel with the shore. These islands are not vestiges of ancient shore lines, the most resistant parts of which have escaped destruction by tie waves; some of tue most important of tnese isles, Belle-Ile for example, are composed of soft schists, more prominent in tneir relief above the sea tuan some of the durable grauitic isles. Tectonic actions have been responsible for their formation, a sinking of tue space between the present isles and the mainland (called le Morbraz, a region formerly fashioned by subaerial erosion.) The sea has not acted in tne same fashion at all points al ong tuis coast. Here it destroys; there it constructs. The materials brought down by the Loire and the Vilaine are carried along tne coust by currents to the north as far as Morbihan. This action has led to tue attachment of many smell isles to tne continent; hence the promontories of Quiberon and of the Croisic. Beyond tune Point de Pemmarch, the folds of 1'Armorique, in- stead of being cut obliquely by the trace of the continental platform, are cut almost at a normal. The singularities of the coast line, which are here most accentuated, may be traced to the tectonic condition of the antique Hercynian peneplain. The Armoricain sandstones and quartzites, being of superior hardness, have formed the Peninsula de Crozon. On the northern framt of 1l'Ammorique, the characteristic features-are the projection of Cotentin and the large rentrant of the Gulf de Saint-Malo. The latter is a sunken region, which, in Miocene times, marked the location of an arm of the sea which cut 1l'Armorique in two. The differential resistance of the hard and soft rocks along this northern coast to wave action, has formed many irregularities in the shore line ~ small embayments and points. Coasts of the Parisian Region:- To the east of Cotentin, the aspect of the coast line changes entirely. No islands or accentuated promontories, but simple lines hard- ly interrupted by the irregularities of the valleys, and which take in places an absolutely massive character. The rocks here form slopes or banks, often grading into almost vertical cliffs; instead of projecting toward the sea, they are arranged in lines parallel with the coast line. of 1'Armorique. In attacking the gentle undulations of the former, the marine erosion has found the same materials disposed in the same fashion over vast stretches, without any of the brusque changes encountered at each step in the compressed folds of tectonic Brittany. Sapping action has worked under almost identical conditions throughout long stretches of the shore line. The divisions of the coast line are an immediate consequence of those divisions which we have identified in the Parisian Region. First we find the depressed coast region of Caretan, an even shore line, where the Hercynian base has been covered by a mantle of diverse Secondary and Tertiary terrains. A cordon of dunes lines the shore, owing their origin to the shelter of the Cape de la Hougue. Further east is the coast of Calvados (see map of Northern France, page 14-15). Here the Jurassic argillaceous beds, being over- lain by a durable limestone, form high eliffs. In the neighborhood of the Orne, the coast again becomes low lying, and is characterized by a line of dunes. Then, in the regions of Auge and le lLieuvin, the cliffs recommence, but with the intervention of Cretaceous rocks which form the covering. The meanders of the lower Seine, now profoundly entrenched, have formed a wide plain adjoining this part of the coast. To the north, the Pays de Caux are terminated by abrupt cliffs, some 100 metres in height. These cliffs truncate all the plateau of Haute Normandie. The estuary of the Somme corresponds to a sharp entrant in { the terminal slopes of the Parisian Region. Ancient littoral deposits form the shore line here, back of which we find a line of dunes; still further inland, the plateaux of Picardie. The Cape Griz-Nez, S.W. of Calais, is formed of Jurassic cliffs. The tectonic folds of the continent are continuous under the All this change is expressive of the contrast which the simple { structure of the Parisian Region presents with the complicated architecture wo fe Pas-de-Calais. Along the North Sea, France has only a short coast line. The Maritime Plain of Belgium ends here, protected by a line of dunes. The strata here show an alternation between marsh or peat deposits and beds of marine origin, indicating repeated changes in the level of the land with respect to the sea. The last of these fluctuations has occur- red as late as the present historic era. The map below shows the traces of the principal undulations of the Anglo-Parisian Region in the vicinity of the English Channel. (1) is the anticline of Leon; (2) the depression of Lessay; (3) the anti- clinal des Huchettes; (4) the anticline of Bray; (5) the syncline of the «© > — ~~). x @™ 9 x: 0) Cuan 4 BY Arras S ¥\ wv a, G-! GI, c ~ perboued : * Xe x . @ Ae Havre x9 xx wv < J ay " & S 2 =x «OZ 4 Xb) ~ * . «* PRS rest © 3 ++ v * ~\ - = nA A hactres Somme; (6) the syncline of l'Authie; (7) anticline of Artois; (8) the anticline of the south of the Isle of Wight; (9) syncline of the north of the Isle of Wight. END OF TITLE