-0 
 
 r * 
 
 
 
Cornell University Library 
 QE 461.C98 
 
 Augite-syenite gneiss near Loon Lake, Ne 
 
 924 004 049 981 
 
 (Rnmll Uttivmitg §ibats 
 
 THE GIFT OF 
 
 J«w^ a? AAM)M:<^^r^ 
 
 A'\^^M_ 
 
 IP 
 
 <i/7/^ 
 
BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 
 
 Vol; 10, PP. 177-192, pls. 19-20 
 
 \UGITE-SYEXrTE GNEISS NEAR LOON LAKE. NEW YORK 
 
 BY 
 
 H. P. CUsni.NU 
 
 ROCHESTER 
 
 PUBLISHED BY THE SOCIETY 
 
 April, 1899 
 
BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 
 
 Vol. 10, pp. 177-192, PLS. 19-20 APRIL 1, 1899 
 
 AUGITE-SYENITE CIKEIS>S NEAR LOON LAKE, NEW YORK 
 
 BY H. P. CURHIXG 
 
 {Read before the Society December 30, 1898) 
 
 CONTENTS 
 
 Page 
 
 Introduction 177 
 
 Megascopic character 178 
 
 Section near Loon lalte and its interpretation 178 
 
 Microscopic character and mineral constituents 180 
 
 Structure of the rocks 182 
 
 Chemical analyses ^ 182 
 
 Table of analyses 182 
 
 Discussion .,183 
 
 Geologic age 185 
 
 Adirondack syenite areas 186 
 
 J^oon lake 180 
 
 Salmon river 187 
 
 Diana . . 187 
 
 Mount Defiance 187 
 
 Big Tupper lake . 188 
 
 Relationship to the anorthosites 188 
 
 Similar petrographic provinces .' . 189 
 
 Canada north of Montreal 189 
 
 Lake Superior 190 
 
 Norway ' 190 
 
 Sequence of eruptions in the Adirondacks 190 
 
 Summary 192 
 
 Introduction 
 
 Field-work in a portion of the Adirondack region during the past two 
 years has disclosed the rather widespread occurrence of rocks which 
 resemble some phases of the anorthosites, and were classed with them 
 until inspection of thin-sections showed their quite different nature. 
 Similar rocks prove to be of frequent occurrence in the district; and to 
 have an extent and importance not heretofore recognized. They also 
 possess considerable intrinsic interest, so that some preliminary notice 
 
 XXYTT-BuT-T Gfot Sor. Am , Vot 10, 1<^08 (177) 
 
ITS 11. r. (^T'sinxG — aititte-nyicxtte (ixetss xkaii loox latck 
 
 of them would seem to be justified in advance of a thoroiioh investio-a- 
 tion of their field relations. These rocks are widely and quite typicall}'' 
 exposed in the vicinity of Loon lake, in Franklin county, New York, 
 and many of the exposures are easily accessible; hence their selection 
 for descriptive purposes. The rocks are referred to the augite-syenites. 
 
 Mkg ^scoprc Character 
 
 When fresh these rocks are of a grayish green color, which quickly 
 changes to a more pronounced green on slight exposure. When longer 
 exposed a further change to a yellowish or In-ownish green takes ])lace, 
 and then a passage into a rusty brown, which is the prevailing color of 
 the exposures, except in recent cuts. The cause of these rapid color 
 changes is not manifest, sections from specimens of the first three shades 
 showing all the constituents to 1)e perfectly fresh. Even the rusty brown 
 rocks are often quite unaltered, though the hypersthene is commonly 
 decomposed, suggesting staining from the oxidation of the ferrous oxide 
 as a possible cause of the color here. 
 
 For the most part the rocks are of medium grain, though with much 
 variation from place to place. They have been subjected to regional 
 metamorphism in common with the other rocks of the district, and 
 hence are rather evenl}^ granular, though in most cases larger crystals are 
 more or less abundant, suggesting cataclastic structure. Feldspar is 
 much the most prominent mineral, constituting usually about <S0 ])er 
 cent of the rock. The uncrushed crystals are always less green than the 
 granular feldspar. Pyroxene or liornblende and quartz make up the 
 rest of the rock. Sometimes a little garnet and magnetite may be dis- 
 cerned. Biotite is locally present. 
 
 As a result of metamorphism, a rude foliation is commonly apparent, 
 though with much variation from place to place, depending on the 
 amount of ferromagnesian silicates present and on the degree of gran- 
 ulation. In other words, precisely the same range is shown that the 
 gabbros exhibit, though very coarsely crystalline phases comparable to 
 the coarse anorthosites have not been observed. In the more quartzose 
 varieties the ferromagnesian silicates retreat with disappearance of the 
 foliation, its place being taken by a rude linear structure due to the 
 drawing out of the quartz into pencils. 
 
 Section near Loon IjAKe and its Interpretation 
 
 In the east end of Loon Lake mountain, south of and within 2 miles 
 of the depot, the Adirondack and Saint Lawrence railroad has made three 
 

 cc. 
 o 
 
 > 
 
 UJ 
 
 o 
 
 O 
 
 UJ 
 
 z 
 
 UJ 
 
 >• 
 
 CO 
 
 
 
 - Z. iC 
 
 
 
 — C ic 
 
 H 2 ^. 
 
 O p 
 
 t Is 
 
 CC X -^ 
 
 _l - - 
 
 < V - 
 
 CC ~ 
 
OKOLOGIC SECTION AND ITS INTKItFKETATlOX 179 
 
 rock cuts, which afford very interesting exposurefcS.'^" In the first cut a 
 fairly coarse augite-syenite is shown which has not been severely gran- 
 ulated, is practically non-foliated, and has a very evident cataclastic 
 structure (plate 19).t The second cut shows quite similar material, 
 though more crushed and with a better foliation. The third cut is 
 quite extensive, and a generalized section of the exposures is given in 
 the accompanying figure. 
 
 The augite-syenite constitutes the center and south end of the section. 
 It is more thoroughly granulated and more gneissoid than in the pre- 
 ceding exposures. Separating the two syenite areas is a thickness of 
 12 feet of well banded gneisses. Above is a hiyer 2 feet thick of a white, 
 granular rock composed of quartz and white pyroxene in the proportion 
 of 1 to 2. This is followed 1)}^ layers of granular, black i)yroxene gran- 
 ulite and light colored quartzose rocks, the latter consisting essentially 
 
 C_ A D B A 
 
 Kn.rur. 1. — ^^'fcfioii in Hailroad (Jut iiuw Loon Lahi\ Xttr York, 
 
 A, uugite-syenitt'. B, well handed quartzose gneis.ses. C\ qtuu'tzo.se ft-neis.ses, D, biotitic 
 sheared strip— strike* north 10 dejj;ree.s west. Dip of Ix'eMiiiij and tbliatioii (m degree^^ to the west. 
 
 of quartz and potash feldspars, the (luartz forming from 60 to 70 per 
 cent of the rock. The structure and composition indicate a sedimentary 
 origin for these included bands, and they ai'e precisely like rocks which 
 invariably accompany the crystalline limestones of the region, the white 
 pyroxene being especially characteristic. At the lower contact Avith the 
 S3^enite is a probable shear- plane, along which biotite is abundantly de- 
 veloped. This syenite is succeeded to the north by finely granular, red, 
 granitic gneisses of doubtful origin, but also very similar to rocks which 
 are of common occurrence associated with the limestones. The foliation 
 planes of the syenite have the same dip and strike as the included 
 gneisses. 
 
 There can be no question of the sedimentary origin of the gneisses in- 
 cluded under ^' B '^ in the section (see plate 20). With that as a start- 
 ing point, the uniform dip and strike in the exposure, together with the 
 finely granular character of the syenite, give the impression that the 
 whole forms a regularly bedded series ; but when the syenite is coni- 
 ])ared with the rock in the other cuts it is seen to be unquestionably the 
 
 *'rhese exposures were visited in eoinpuiiy with I^rofos^or A. ('. Ixill iu July, 1<S97, and with 
 Professor J. F. Kemp in August, 18U8, neither of whom objected to the interpretation here given. 
 
 t A photograph of this exposure is reprodu<*e<l iw jilate U) to indicate the color change due to 
 weatliering. 
 
180 H. p. CUSHIX(4 AUUTE-iSYENlTE (^NKIbb XEAJl LOON LAKE 
 
 same, and that appears like a bomewhat crushed intrusive rock. When 
 it is recalled that the whole region has suffered profound dynamic met- 
 amorphism, producing a common foliation in the rocks irrespective of 
 their origin ; when it is further borne in mind that in the eastern half 
 of the Adirondacks the rocks of the Grenville (crystalline Hmestonej 
 series sehlom occur in considerable belts, but rather in mere patches, 
 and these ])atches are often wholly surrounded by undoubted igneous 
 rocks, being found not infrequently inclosed in the anorthosites, and, 
 further, that in the majority, if not in all cases, the bedding of the one 
 and the foliation of the other are parallel, the seeming difficulty in the 
 interpretation diHa])pear& ; when, finally, the chemical nature of the 
 rock is taken into consideration the case for its igneous origin seems 
 made out. 
 
 It is not certain from the section whether the clastic rocks are in place 
 and cut by large dikes of the intrusive, or wdiether they represent frag- 
 ments caught up by the molten flood. Many examples of the latter 
 might be cited from the eastern Adirondacks, and the great extent of 
 the syenite in the vicinit}^ of Loon lake with the scarcity of the Gren- 
 ville series makes it the probable explanation here. Professor Kemp 
 concurs in the view^ that these patches represen*t the remains of a once 
 extended formation completely broken up by the great intrusions. 
 
 Microscopic Character ano IMtneral Con&tituexnts 
 
 The thin-section from the hand specimen chosen as typical and used 
 for the chemical analysis shows the presence of the following minerals : 
 Zircon, apatite, magnetitCj garnet, hypersthene, augite, hornblende, oligo- 
 clase, microperthite, and quartz. Other slides from the vicinity of Loon 
 lake show in addition biotite, titanite, allanite, and pyrite. The rock is 
 essentially composed of microperthite, augite, and hypersthene, with 
 quartz always present in vax-ying and commonly slight amount. 
 
 Zircon and apatite are very sparingly present, are the only constit- 
 uents with idiomorphic boundaries, and occur in the usual microscopic 
 crystals as the earliest crystallization from the magma. 
 
 IMagnetite is only in slight amount in irregular grains. 
 
 Allanite and titanite are found in only one of the slides and in only 
 minute quantity. The titanite is of deep orange-brown color, like that 
 in the pyroxene-granulites found associated with the magnetites of the 
 Adirondacks. But two small fragments of allanite occur, so that its 
 diagnosis is perhaps not beyond question, though the optical properties 
 agree wholly with those of that mineral. 
 
BULL. GEOL. SOC. AM. 
 
 VOL. 10, 1898, PL. 20 
 
 BANDED GNEISS INCLUDED IN AUGITE-SYENITE 
 The hammer is at the contact. Photographed by J. F. Kemp August 2, 1898 
 
:\IICH0SCUP1C ClIAKACTEll ANJJ Ml^EKAL COXfoTlTUENTS 181 
 
 Garnet occurs only sporadicall}^ and is not idiomorphic, but appears 
 in reaction-rim fashion between the magnetite and feldspar, sending out 
 tongues into the latter mineral. 
 
 Of the pyroxenes, both hypersthene and augite are present, the latter 
 usually predominating. Parallel growths of the two frequently occur, 
 often of repeated line lamella.^ the contact faces being as usual. Other 
 growths appear also, and sometimes one mineral is found wdiolly in- 
 cluded in the other, each appearing in that condition- Their boundaries 
 are never idiomorphic, but always irregular and more or less rounded. 
 
 The hypersthene is quite typical, except that the prismatic cleavage 
 is more pronounced than the ])inacoidal. The augite recalls diallage in 
 some respects, but the ])inacoidal cleavage is absent or but poorly 
 developed. The color is green, wuth a very slight pleochroism in the 
 thicker slides, 6 having a yellowish tinge. The ordinary color is very 
 similar to the green of the hypers thene. Besides the prismatic cleavages 
 there is a w^ell developed parting parallel to the base. The extinction 
 angle is between 45 and 50 degrees. 
 
 In the rock immediately under discussion hornblende is found in 
 very slight quantity, though elsewhere present in considerable amount. 
 Like the pyroxene, it appears in irregular grains, though sometimes there 
 is an approximation to idiomorphic outhnes. The absorption and ]>le- 
 ochroism are very strong, a being pale yellowish, Ji deep brow^n, and 
 f dark green, with l)>f>a. Tlie 6 color is very like the brown of the 
 biotite, which also occurs sparsely in the more hornl^lendic rocks. 
 
 Tlie feldspar is almost wholly microperthite. A few grains of plagio- 
 clase always appear and invariably extinguish nearly parallel to the 
 trace of the albite twinning lamella). The greatest departure from 
 parallelism in any of the slides was 7 degrees. In no other case does it 
 reach 4 degrees. These fragments must therefore be referred to oligo- 
 clase. The chemical anal3''sis shows that the plagioclase ])resent must, 
 as a whole, ])e considerably more acid than normal oligoclase and nearer 
 to albite. 
 
 The feldspars are very fresh. They contain a small amount of cloudy, 
 dust-like inclusions, and also include the zircon, apatite, titanite, and 
 small augites, tliese latter being exceptional and idiomorphic. They also 
 include small, idiomorphic or else rounded quartzes, as determined by 
 Becke's method. 
 
 Orthoclase is only present as a constituent of the microperthite. 
 There is no indication of zonal structure — that is, microperthite with 
 oligoclase cores — as in the similar rock described by Smyth from Diana.-'^ 
 
 *C. H, Smyth, Jr. Tlub Bull., vol b, pp. 271^^74. 
 
182 H. p. CUSHlX(i — AUdlTE-SYEXiTE (iXEISS NEAll LOON LAK K 
 
 (iuartz occurs only sparing!}^ in this rock, though very quartzo.se 
 phases appear elsewhere in the Loon Lake vicinity. It is niainl}'' in 
 rather large, elongated, cylindrical individuals. The elongation seems 
 to he effected rather by solution and recrystallization than by crushing. 
 The individuals are either entire or made up of but few fragments, and 
 the line granulation which must have been produced by the crushing 
 process is nowhere in evi<lence. In the quartzose varieties the ferro- 
 magnesiau silicates recede with disai)pearance of the foliation, its place 
 being taken by a linear structure produced by the elongated quartzes. 
 
 Some quartz is also found as inclusions in the feldspar, sometimes 
 rather numerousl}?' and with a tendency to micrographic growths. There 
 is also a small amount of interstitial quartz and orthoclase, which seems 
 secondary, 
 
 Structure of the Rocks 
 
 These rocks have a cataclastic structure. In the gneissoid rock, from 
 the third cut the granulation is pretty complete, but even there occa- 
 sional larger nuclei remain and show ixndulatory extinction. In the 
 coarser rock, from the first cut many such large fragments are found, 
 constituting more than half the rock. The Diana rock shows the struc- 
 ture even better. Precisely the same variations in degree of granulation 
 are to be found that the anorthosites exhibit, except for the lack of the 
 very coarse varieties in the syenite, such as make up a considerable part 
 of the anorthosite, but this is regarded as an original difference. In 
 addition to the cataclastic structure, the rock is nearly everywhere 
 foliated. 
 
 v^llEMlOAXj j.!LN ALi I Sliife 
 TA BLE OF A NA L Y^E^S 
 
 These syenites are so variable in minei'al content and their field rela- 
 tions to other rocks, which on the one hand are much more acid and on 
 the other more basic, and into which they apparently grade, are yet so 
 uncertain that a large amount of chemical work will be necessary in order 
 to full^^ elucidate the problems suggested. Only a beginning has been 
 made in this, which, however, suffices to show the character of the typical 
 rock and to permit of a certain amount of discussion and comparison 
 with other syenites. 
 
TABLE OP ANALYSES 
 
 1Qt> 
 
 1 
 
 J. 
 
 XL 
 
 TIL 
 
 1 
 
 65.43 1 
 0.50 
 16.11 
 f 1.15 
 t 2.85 j 
 0.23 ' 
 1.49 
 0.03 
 0.40 
 5.97 
 5.00 
 0.13 
 
 0.78*i 
 
 j 
 
 IV. 
 
 V. 1 
 
 VL 
 
 vri. 
 
 SiO., 
 
 TiO, 
 
 (>3.45 
 0.07 
 
 18.31 
 0.42 
 3.56 
 
 None. 
 2.93 
 0.13 
 0.35 
 5.15 
 5.06 
 
 Trace. 
 0.30 
 
 65.65 ' 
 '1*6. 84' 
 
 66.60 
 0.76 
 15.05 
 1.07 
 4.42 ' 
 Trace. 
 2.21 
 
 ' * ' b'.36 
 5.42 
 4.03 
 
 * * ' 0*41 
 
 66.13 1 
 0.74 
 17.40 
 
 } 2.19 1 
 
 0.13 
 O-Sl 
 
 59.78 
 
 64.35 
 
 Al,(3i 
 
 16.36 
 f 3.08 
 I 3.72 
 
 2.96 
 
 15,46 
 
 FeA 
 
 FeO 
 
 MnO 
 
 }7.50 
 
 CaO 
 
 BaO . ... 
 
 2.47 
 
 
 "0.13* 
 5.04 
 
 5.27 
 
 i 
 
 0.36' 
 
 3,58 
 
 M2O 
 
 0.04 
 5.60 
 5.28 
 
 "V.22' 
 
 0.69 
 5.01 
 5.39 
 CO2 0.75 
 1.58 
 
 0.50 
 
 K,0 
 
 Na.,0 
 
 3.45 
 3.28 
 
 P2O3 
 
 Los« 
 
 
 
 
 99.73 
 
 99.71 
 
 100.18 
 
 100.33 
 
 99.54 
 
 99.96 
 
 99.84 
 
 Specific gravity of number I is 2.717 at 20*^ centigrade. 
 
 I. Augite-syenite (akerite), Loon lake, New York. Analysis by E. lY. Morley.f 
 
 XL Augite-syenite (akerite) from Diana, New York. Debcription and analysis 
 by C. H. Smyth, Jr., in this Bulletin, vol. vi, pp. 271-274. 
 
 III. Syenite, mount Ascutney, Vennout. Petrographical data by Tl. A. Daly, 
 analysis by L. G. Eiikins, in U. S. Geological Survey Bulletin no. 148, p. 68. 
 
 I Y. Akerite, Gloucester, Massachusetts. Description and analysis by H. S. Wash- 
 ington, in Journal of Geology, vol. vi, p. 798. 
 
 V. Akerite, between Thinghoud and Fjelebua, Norway. Analysis by Mauzelius, 
 descrii>tion by Brogger, in Zeitschrift fur Ivrystallographie, vol. xvi, p. 4(), 1890. 
 
 YI. Syenite, Silver Cliff, Colorado. Description by Whitman Cross, analysis by 
 L. G. Kakins, in 17tli Annual Report, U. S. Geological Survey, part ii, p. 281. 
 
 YIL Banatite, Farsund, Norway. Description and analysis by Carl Fred. Kol- 
 derup, Bergens Museums Aarbog, 1896, p. 213. 
 
 TXie Loon Lake rock (column I) is composed of microperthite, aiigite, 
 hypersthene, and quartz, with a little magnetite and oligoclase, and such 
 small amounts of apatite and zircon that they in no vi^ay affect the totals. 
 With this comparatively simple make-up it would seem an eagt}^ matter 
 to calculate the composition of the rock. It soon appears, however, that 
 the augite must be peculiar, and that a wholly satisfactory calculation 
 can not be made until it has been analyzed. It must be either very rich 
 in iron or alumina, or both, or else contain considerable alkali, but its 
 optical characters are not those of any known alkaline pyroxene. Further, 
 the available analyses of aluminous augites show that a high alumina 
 percentage usually implies a large content of ferric iron, which is mani- 
 
 * Includes F, 0.08, 01, 0.05; FeSo, 0.07, 
 
 fThe gieat obi jj^at ions of tlie writer to Professor Moiley tor this analysm arp giatefullyacknow I- 
 edged. 
 
184 H. p. ri'SHTXG — ArGITE-SYKNITE GKKTSS XEAE LOOX LAKE 
 
 lestly iin])0ssibl<» here. The only way of iiit(^rpreting- the analysis that 
 suggests itself to the writer is to assume that the augite is essentially a 
 lime, ferrous-iron, alumina silicate, unusuall}^ high in the last named 
 oxide. 
 
 Cnhahdlon <{( A iKiit/xix 1 
 
 lai 
 
 8iO, 10575 
 
 TiO; 9 
 
 ALOj , 1795 
 
 FeA 25 
 
 Feb I 494 
 
 HtiO 8 
 
 Oi(; 52;] 
 
 :SU^O 87 
 
 K.,0 ^ 547 
 
 Ka,0 i SU 
 
 Molec'u- Magno- Ortlio- ,„„•.„ AiKir- 1 Hj'per- 1 ,„„,•.„ ' />nnrf-/ 
 :arrati<..l tiTe. clanp. '^''"^'^- thite. ' sthene. ' *-^"8''^''- i *^"'^"'^- 
 
 9 
 
 :]-js2 
 
 4890 
 
 ;]18 
 
 17i 
 
 745 ' 
 
 1 
 
 IKJO 
 
 26 
 
 35 
 
 
 
 547 
 
 81(> 
 
 159 
 
 
 0/2 1 
 
 
 
 
 
 87 
 
 :]72 1 
 
 
 
 
 
 .8 
 151 
 
 
 
 
 87 
 
 r'j72 ' 
 
 
 
 547 
 
 '"816 
 
 
 
 
 
 
 1 
 
 
 
 
 0.7;] 
 
 30.;]9 
 
 42.70 
 
 4.51 
 
 2.02 
 
 12.02 1 
 
 1 
 
 7.07 
 
 This result agrees quite well with that ohtained by separation with 
 heavy solutions, and can not be far from the actual composition of the 
 rock. As it stands, the plagioclase is albite, Abjj, An^, and the micro- 
 perthite is ai)proximately Or.^ Ab.. The plagioclase is in all probability 
 not quite so acid as this would imply, as the augite undoubtedly contains 
 a little soda, wdiich would disph\ce some of the lime calculated in that 
 mineral, and both lower the albite and raise the anorthite i)ercentage. 
 It is thought that this change is onh'' slight, not materially affecting the 
 calculation. 
 
 The agreement between analyses I and II is exceedingly close. The 
 Diana rock is even more feldspathic than that from Loon lake, which 
 accounts for the increased silica and diminished lime and magnesia of 
 the former; but the rock at Loon lake is quite variable, and specimens 
 could be selected which would tally almost exactly with the Diana 
 analysis. No doubt also the converse is true. 
 
 Of the other available published analyses of American syenites, the 
 two which stand nearest the Adirondack rock are quoted in columns III 
 and IV of the table. Of the Mount Ascutney syenite, no published petro- 
 graphic description is available.* A hand specimen and slide in the 
 writer's possession show a green feldspathic rock very similar to that 
 
 * J)r Daly partieipiited in the discussion following the reading of the paper before the Society, 
 stating that the relations of the roeks of mount Ascutney had been carefully worked out and were 
 in preparation for publication, and emphasizing the similarity of the Loon Lake rock. 
 
DISCUSSION OF ANALYSES 185 
 
 from Loon lake except for its freedom from nietamorphism. Hyper- 
 sthene is lacking, and there is rather a predominance of hornblende over 
 augite. which latter is colorless instead of green. Chemically it is closer 
 to the rock from Diana than to that from Loon lake, but is lower in 
 lime and magnesia than either. The agreement is, however, very close. 
 
 Likewise the syenite from Essex county, ^lassachusetts, just described 
 anew by Mr. H. S. Washington, shows great similarity with the preceding.* 
 It lacks hypersthene, and the augite is like. that in the Mount Ascutney 
 rock. The specimen analyzed is more acid than the Adirondack rock, 
 with lower alumina, higher iron, and slightly lower alkalies, with the 
 potash somewhat in excess of the soda. These differences are all slight, 
 and of the essential identity of the rocks there can be no question. As 
 stated b}^ Washington for the Massachusetts rock, all belong to the variety 
 of augite-syenite called " akerite " b}'- Brogger and the '' akeritetype " by 
 Rosenbusch — in other words, are quartzose augite-syenites. The analysis 
 quoted by Washington of an akerite from Norwa}'' (column V) is ap- 
 pended, though, as stated by him, it is an acid representative of the 
 group. Furthermore, it is unusually low in lime, much more so even 
 than the Mount Ascutney rock. The analyses bring out clearly the con- 
 siderable variation to which these rocks are subject. Not improbably 
 they could all be duplicated in each locality. 
 
 All the rocks represented in the first ^ve analyses are quartz-syenites 
 and quite acid representatives of the syenite group, approaching the 
 acidity of granites. Column VI gives an analysis of a more normal 
 syenite, introduced merely to empha«?ize the departure of the others 
 from the ordinar}'' type. 
 
 Banatite is the name given by Bnigger to rocks of the monzonite 
 group (orthoclase-plagioclase rocks) which range between 62 and 67 per 
 cent of silica. The analysis (column VII) will indicate the differences 
 between them and these akerite-syenites, namely, the higher amount of 
 lime and magnesia and lower alkalies. Rocks of the monzonite group 
 are widely exposed in western Norway, a petrographical province which 
 has many features in common with tbe Adirondacks, in close associa- 
 tion with rocks of the gabbro group, anorthosites, norites, and so on. 
 They have recently been exhaustively investigated by Kolderup,t and 
 will be reverted to later. 
 
 Geologic Age 
 
 Quite fortunately the exposures in the railroad cuts near Loon lake 
 furnish data for a rough determination of the age of the syenite. For 
 
 * Jour. Geology, vol. vi, pp. Y96~798. 
 
 t Bergens Museums Aarbog, 18')C, no. V. 
 
 XXViri—BuLL. Geol. Soc. Am., Vol. 10, 1898 
 
18() IL V. (TSHIXlr — Ar<,ITK-SYEXITE (JXKISS NKAK LOON LAKE 
 
 a lon^ ixn-iod hefbre the deposition of the Potsdam sandstone the Adiron- 
 dack region was above sealevel, so that none l>ut igneous rocks are found 
 representing the time interval between tlie Potsdam and the only older 
 sedimentary formation known in the district, the crystalline limestones 
 and associated qiiartzites and gneisses. These latter are evidently the 
 equivalents of the Grenville series of Canada. The syenites are younger 
 than the Grenville rocks, for they cut or include them, as already noted. 
 On the other hand, they are older than the youngest of the pre-Potsdam 
 rocks, the diabases, for tliey are cut by them. In the first cut, 100 rods 
 south of the depot at Loon lake, the syenite is traversed by a diabase 
 dike o ieei wide. 
 
 These diabases have not ])een metamorphosed, wdiereas the syenites 
 have suffered change of such a character as to indicate that during the 
 process they were deeply enough buried beneath deposits since eroded 
 away to be in the zone of flow", so that a long time interval must lie 
 between the two. In addition to these syenites, the gabbro rocks and 
 certain granites are later than the Grenville rocks and much older than 
 the diabases. The relationships of the gabbros, syenites, and granites 
 to one another wnll be reverted to later. It should be stated that they 
 are older than the Essex county, Massachusetts, rocks, wd)ich cut Lower 
 Cambrian strata, according to 8ears,'^ and are likely older than the 
 ]\Iount Ascutney syenite as w^ell. 
 
 Adirondack Syenite Arkas 
 
 loon lake 
 
 The Loon Lake syenite belt is quite extensive, having a length of 
 nearly 20 miles and a breadth of 10, though of irregular shape. These 
 figures are advanced with some hesitation on account of the difficulty 
 of recognizing the rock in ordinary exposures, especiahy tow^ard the 
 periphery of the belt. It is only in recent cuts that fresh material is to 
 be obtained. In ordinary outcrops a rusty, brown gneiss prevails, wdiich 
 may or may not shoAv greenish, less weathered nodules when broken. 
 The much elongated character of the quartz- augen often shows character- 
 istically in these weathered rocks, and considerable dependence has been 
 placed upon it as k criterion for their recognition ; but this is only of 
 avail in the more acid phases, whereas the fresh rocks are found to pass 
 into varieties in wdiich the ferromagnesian silicates become more promi- 
 nent and quartz recedes. Weathered rocks of this type have a wide 
 range. They are finer grained and better foliated than the type and, 
 
 *J, H. Sears : Bulletin Essex Institute, vol. XXII, 1890. 
 
ADIKOXDACK SYEXTTK AIIEAS 187 
 
 when weathered, are absolutely not to be cliBtingiiished from other rocks 
 of apparently quite different relationships. 
 
 A variation is also shown in the opi)osite direction. Belts of very 
 acid, red granitic gneisses consisting essentiall}^ of microperthite and 
 quartz, with or w^ithout hornblende and augite, occur in the syenite- 
 gneisses and seem to grade into them. For the most part they differ 
 greatly in appearance from the usual granitic gneisses of the Adiron- 
 dacks, being of coarse grain, with the quartz in the much elongated form 
 in wdiich it is found in the syenite-gneiss. These rocks are not so w^ell 
 shown in the Loon Lake belt as in others to he luentioned. The seem- 
 inq gradation of the one into the other, the identity of the horn))lende 
 and augite, when they occur, in the two rocks, and the peculiar type of 
 quartz are the reasons for assuming a near relationship to one another. 
 
 SALMOX EIVER 
 
 A smaller belt of syenite-gneiss, some 6 miles long and 2 miles broad, 
 runs from a point about 7 miles south of Malone down into Duane town- 
 ship. It is cut through by the Salmon river and the rocks well ex- 
 posed, especially at Chasm falls. The fresh green gneisses are quite like 
 those at Loon lake; but red gneisses make up a more considerable i)art 
 of the exposures here, and in part the color is produced b}^ weathering, 
 instead of indicating a more acid rock. As a whole, hornblende is more 
 prominent and p3^roxenes less so in this belt, but no other differences 
 appear and the identity of the rocks is beyond question. The only 
 doubt is in regard to their areal extent, as they fade out into other rocks 
 through puzzling intermediate phages. 
 
 DIANA 
 
 According to Smyth the Diana s^^enite belt is fi^om 15 to 20 miles long 
 and 2 to 4 broad, with very indefinite limits on all sides but the north .-^ 
 To the south patches of it appear frequently in the midst of gneiss, into 
 which it seems to blend, although the relation is obscure. Irruptive 
 contacts with the limestones of the Grenville series are well shown, es- 
 pecially at Bonaparte lake. Professor Smyth writes me that he has 
 found no other large area of this rock in the western and southern 
 Adirondacks, though occasional small patches occur, with a wide range 
 in distribution.'!" 
 
 MOUNT DEFIANCE 
 
 Professor Kemp has called my attention to the probable identity of 
 
 *C. H. Smyth, Jr. : This Bull., vol. vi, pp. 27W74. 
 
 t An extended description of the Diana belt will be fouutl in Prufc&Nor bmyth'fo forthcoming 
 report in the 17th Aiin. Rep, State Geologi&t of New York, 
 
188 H. I*. CUSHJXG — AKxJTE-hYENJTE (xXEJSfe XEAK LOON LAKE 
 
 the rock which constitutes mount Defiance, near Fort Ticonderoga, with 
 these syenites, and inspection of his specimens and slides fully confirms 
 the suggestion. Here also hornblende is more prominent than at Loon 
 lake, but the characteristic augite is also conspicuous. Allanite occurs 
 here likewise.'^ 
 
 BKf' n PPER LAKE 
 
 Rocks which are at least in part to be classed with these augite-syenites 
 are excellently ex2>osed along the shores of Big Tupper lake and extend 
 widely to the north and east. They are closely involved with red gra- 
 nitic gneisses which equal them in extent and into which they grade. 
 Together with these are other granites, of whose relations nothing can 
 be said, as no contacts have been seen. 
 
 Relationshii* to the Anorthosites 
 
 The main interest attaching to the Tupper Lake S3^enite lies in the 
 evidence it may be expected to furnish concerning the relations of the 
 syenites to the anorthosites. A large area of anorthosite in southern 
 Franklin county, in the heart of which the Saranac lakes lie, is sur- 
 rounded by the Tupper Lake syenite on the south and west. 
 
 It may be said, in the first place, that the syenite cannot differ greatly 
 in age from the anorthosite, having been intruded into the Grenville rocks 
 and subsequently metamorphosed under the same conditions as to load, 
 as shown by the character of the metamorphism. Again, their areal dis- 
 tribution indicates consanguinit}^ Further, the identity of many of the 
 minerals in them and in the granitic gneisses as well combines to render 
 it strongly probable that all have resulted from a common magma. 
 
 With such ideas in mind, a series of traverses were attempted from 
 one to the other, which were unsatisfactory, owing to a lack of outcrops 
 at the more crucial points. In some cases a blending of one rock into 
 the other seems apparent in the field. The anorthosite becomes much 
 crushed and very gneissoid near the peripheral parts of the mass, the 
 blue labradorite-augen showing constant decrease in number and eventu- 
 ally disappearing entirely. When fresh these crushed rocks are much 
 like the syenite in color and appearance, and weather into brown gneisses 
 the exact counterparts of the weathered syenites, so that it is impossible 
 to tell when the passage from one rock to the other is made, but the thin- 
 sections do not wholly bear out the idea of such a blending. Anortho- 
 sites are found which contain both orthoclase and quartz, denoting an 
 
 * J. F. Kemp : Rep State <kH)l. N. Y. IHi),], pt. i, p. 452. 
 
KELATlUXSlllP TO THE ANOKTHOblTKb 1 8U 
 
 approach toward the syenite, but no strictly intermediate varieties are 
 yet forthcoming. 
 
 In other places the passage from one rock to the other is quite abrupt, 
 with no sign of blending. Unfortunatel}^ no contacts have been noted, 
 so that there is nothing to show which rock is the older. In two or three 
 instances what seem to be small inclosures of unmistakable anorthositc 
 in the syenite have been noted, but in each the latter is far from fresh 
 and there is some question of its identit3^ 
 
 The fact that areas of each are found wholl}^ apart from any trace of 
 the other is good evidence for the separate nature of the intrusions ; nor 
 is there any reason wh}^ differentiation should not have taken place for 
 the most part ])efore the intrusion of either, and yet that a fux^ther differ- 
 entiation of local character should not also take place in parts of the 
 anorthosite after reaching their present resting place and while yet un- 
 cooled. 
 
 SiMlLAK PeTROGRAPHIC PROVINCES 
 (UNA DA NORTH OF 3WN TUBAL 
 
 The rocks of the Adirondacks are most naturally compared with those 
 of Canada to the north, being separated from them by a comparatively 
 narrow belt of Paleozoic rocks, beneath which the two are undoubtedly 
 continuous. That rocks corresponding to these syenite-gneisses are 
 present there is undoubted, though as 3"et no attempt has been made to 
 differentiate them from the other gneisses of the region. This is not sur- 
 prising, considering the difficulty of the task and the nature of the country 
 to be explored. 
 
 Adams has described the Saint Jerome anorthosite as 
 
 '* Surrounded by a zone of rocks of varied character, many of which strongly 
 resemble the anorthosite in appearance, but are quite different in composition," 
 and which " consists chiefly of rocks which, in addition to augite and plagioclase, 
 contain variable amounts of hornblende, orthoclase, and quartz, and which are 
 thus intermediate in character between the gneiss and the anorthosite, some of the 
 many varieties represented approaching more nearly to gneiss and others more 
 nearly to anorthosite in character and composition." * 
 
 He expresses the opinion also that the zone is to be regarded as a 
 peculiar border facies of the anortliosite. If this be the true explanation 
 and the writer is correct in his correlation, the area furnishes evidence of 
 the passage of one rock into the other of much more decisive character 
 than any yet forthcoming in the Adirondacks. 
 
 * F. 1). Adams : GeoL Surv. Can., Ann. Rep., \ol. vui, 1S9C, pt, J, p. 121 
 
lUi) if. p. CrSilTNG — Ar(JTE-SYEXlTE (.NKIt^S NKAJt LOON LAKE 
 
 In the same report a number of pyroxeiiic gneisses are described as of 
 doubtful origin, and some of them may belong here, though the majorit.y 
 of them are clearl}^ referable to x\dirondack types, which have nothing 
 to do with the rocks under discussion * 
 
 There are further described from many localities granitic gneisses -with 
 elongated <|uartzes, *' leaf gneisses," which seem in part identical wnth 
 those which appear in the Adirondacks associated with the syenite 
 gneisses as apparent extreme phases of th-e magmatic differentiation. 
 
 LAKE XI FElilOIi 
 
 Though the geological record preserved in the rocks of the Upper Lake 
 region is a much more complicated and complete one than that to be 
 read in the Adirondacks, still there is a close parallelism in the eruptive 
 rocks of the two districts, as has frequently been urged by N. H. Win- 
 chell. Similar syenitic rocks also occur there with the same close rela- 
 tionship to the gabbros, so far as can be told from the descriptions, and 
 have been described by Wadsworth and others. 
 
 Kolderup has recently described exhaustive! 3" a most interesting series 
 of rocks which occur in the vicinity of Ekersund and Soggendal, in west- 
 ern Norway .f Unlike the other two Norwegian anorthosite areas, this 
 one has not suflfered regional metamorphism, so that the field relations 
 are exceptionally clear. He shows that the original magma of the dis- 
 trict has produced by differentiation anorthosite, norite and quartz- 
 norite, and tlie various members of the monzonite group (orthoclase- 
 plagioclase rocks), monzonite, banatite, adamellite, and granite. The 
 order of appearance, according to Kolderup, was first anorthosite, then 
 norite and monzonite, later adamellite and granite, and finally banatite, 
 with no considerable interval of time between any but the first and sec- 
 ond. Last of all and considerably later are dikes of diabase and augite 
 granite. All these rocks agree closely in their mineralogy with the Adi- 
 rondack eruptives. 
 
 Sequence of Eruptions in the Adirondacks 
 
 It is yet too early to attempt any complete discussion of the Adiron- 
 dack igneous rocks, and, owing to the excessive regional metamorphism, 
 it is an exceedingly difficult problem to work out the details of their 
 
 * Ibid., pp. G7-82 
 
 fCiirl Fred. Kolderup. Dd-^* lMl>radorfels i^ebjel; Ijtn Ekcisuiul uiul Sot^geodal, Borgei|s Mu- 
 seums Aarbog, l&OC), 
 
SKQT^EXOE OF ERI'PTTOXS IN THE ABIROXDArivR 19] 
 
 liistory, 1)ut the similarity with the Norwegian rocks just mentioned is 
 so great that it demands notice. The anorthosites are common to both 
 regions. The norites and quartz-norites are also represented in the Adi- 
 rondacks, partly as peripheral phases of the anorthosites which were 
 undoubtedl}^ produced by differentiation in place, and partl}^ as some- 
 wdiat later eruptions which cut the anorthosites and also the older 
 gneisses, but wdiich have not been noted cutting the syenite-gneisses. 
 These norites grade into very basic ilmenite-norites and into quite pure 
 masses of ilmenite in both regions. 
 
 The rocks of the monzonite group are represented in the Adirondacks 
 by the syenitic and granitic gneisses here discussed. These rocks have 
 certainly a range in silica percentage sufficient to include the banatites, 
 adamellites and granites of Ekersund-Soggendal, and as far as can be 
 judged from thin-sections the more basic monzonite end of the series is 
 represented as well. In these rocks we meet the first considerable 
 difference in the two districts. The Adirondack rocks, so far as chem- 
 ically studied, i^un too low in iron, magnesia and lime, and too high in 
 alkalies to be classed in the monzonite group (see analysis VII of the 
 table), though the corresponding niineralogic difference is mainly to be 
 seen in the character of the plagioclase, which is oligoclase in the latter 
 and albite in the former. This likely points to some slight difference 
 in the composition of the original magma, but the general resemblance 
 is so close as to be very striking. Finally, in both regions the eruptive 
 activity closed at a later period with the formation of diabase dikes 
 accompanied by more acid rocks, syenite-porphyry in the Adirondacks 
 and augite-granite in Norway. 
 
 A word of comparison with the Essex county, Massachusetts, ])etro- 
 graphical province may not be amiss. The igneous rocks of the latter, 
 according to Sears, consist of granites, syenites, and quartz-syenites, 
 nepheline-syenites, essexites, diorites, and gabbros, all of which are cut 
 by numerous dikes.-^ Leaving out the nepheline rocks, these are the 
 same types as occur in the Adirondacks ; but when the relative pre- 
 ponderance of the different varieties in the two provinces is taken into 
 consideration it is clear that the original magma in the Adirondack 
 region must have ])een considerably the more basic of the tw^o, being 
 lower in silica and the alkalies and higher in lime and magnesia; 
 hence the prominence of gabbros in the one and of alkaline syenites in 
 the other. Notwithstanding this considerable difiference, some almost 
 identical rock types appear in each as a result of differentiation. It is 
 of interest to note that the two areas present almost precisely the same 
 
 * J. JI. Seals m Bulletin Essex Institute, vol xxvii, 1S95. 
 
192 HP rr'SHixG — vugttk-syf.xite gneiss near loon lake 
 
 contrast to one another that i^ eN:hihited by the Christiana and Ekersund- 
 Soggendal di«?tricts of Norway> 
 
 Summary 
 
 1. A <|uartz-augite <^yenite gneiss near Loon lake is described ti^^ regards 
 its field relations and megascopic and microscopic characters. 
 
 2. Chemical analysis shows it to be a member of the syenite group 
 and an acid representative of the variety called akerite by Brogger 
 
 3. It is shown to be nearly related to the anorthosites m age, inas- 
 much as it is intrusive in the Grenville series, but much older than the 
 ]>re-Potsdam diabases of the region. 
 
 4. Other Adirondack localities are briefly described, and the rock is 
 shown to vary within quite wide limits, ranging from a granite to syenites 
 more basic than the one analyzed. 
 
 5. The relations of the syenites to the anorthosites are discussed, show- 
 ing a lack of decisive evidence, but indicating that syenites are in part 
 a result of differentiation in the anorthosite magma after reaching its 
 place of final coolmg and in part are somewhat later in date. 
 
 6. Comparison is made with the similar petrographic provinces of 
 Canada north of Monti*eal and of Ekersund, Norwa}^ followed by a dis- 
 cussion of the order of eruption of the Adirondack eruptives, which is 
 anorthosites, norites and diabasic norites, syenites, and granites, followed 
 later by diabases and syenite porphyries. 
 
 7. A brief comparison with the Es«ex county, Massachusetts, province 
 suggests that the original magmas in the two districts were quite different, 
 yet another instance is added by them to the many already known of 
 very similar rocks produced by the differentiation of quite dissimilar 
 
 magmas. 
 
 *see Koldeiup, lot < it , pp 191-104 
 
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