SCIENCE. 



[N. S. Vol. XII. No. 290. 



Lake George, and at a point five miles west 

 from the lake shore, the interesting graphite 

 mines have been opened, which show un- 

 doubted fragmental sediments. A bed some 

 6 to 15 feet thick has been faulted once so 

 as to be exposed in two places. It dips to 

 the west at an angle of 10 degrees and 

 contains abundant flakes of graphite, all of 

 which show a rubbed and streaked appear- 

 ance from much mashing and shearing. 

 The rock contains little else than quartz 

 and graphite and cannot reasonably be in- 

 terpreted otherwise than as sandstone, 

 which has been richly charged with some 

 carbonaceous matter, either originally or- 

 ganic or subsequently introduced as some 

 hydrocarbon. Walcott has significantly re- 

 marked that the openings look exactly like 

 a coal mine in pre-Cambrian strata. Be- 

 neath and above the graphitic quartzite is 

 a garnetiferous gneiss, richly charged with 

 sillimanite. Above the upper sillimanite 

 gneiss is still more quartzite and all rest on 

 a granite gneiss. I interpret the succession 

 as one which involved a sandstone, porous 

 enough to admit the carbonaceous matter 

 now represented by the graphite, and inter- 

 stratified in a somewhat calcareous, sandy 

 shale now changed to the garnetiferous, 

 sillimanite gneiss. Whether the lower 

 granitic gneiss is an intrusive, which has 

 developed these minerals by contact meta- 

 morpliism or not ; or whether it was the 

 old foundation on which the sediments were 

 laid down is an obscure question, which I 

 am unable at present to positively decide. 

 The minerals involved are produced both 

 by regional and contact metamorphism. At 

 one point near the mines some small amount 

 of limestone has been revealed by an ex- 

 ploring drill hole, at a shallow depth (30 

 feet) and on the whole I have been more 

 inclined from the evidence in hand to con- 

 sider the granitic gneiss as the foundation 

 on which the sediments were deposited. 

 The largest exposure of quartzite yet re- 



corded is in the town of Lewis, about three 

 miles north of Elizabethtown, in Essex 

 county. Ledges occur more or less charged 

 with graphite and so metamorphosed as to 

 resemble vein quartz, but stratigraphically 

 they have a good dip and strike and they 

 run under gneisses of which I shall later 

 speak. The dip of the quartzite is about 

 10 degrees and the thickness across the 

 stratification is about 100 feet. The gen- 

 eral relations leave little doubt that we are 

 dealing with an old sandstone, somewhat 

 bituminous, and now thoroughly recrystal- 

 lized. All around are great intrusions of 

 gabbros, anorthosites and syenitic eruptives 

 so that the quartzite remains practically as 

 a little island in the midst of an eruptive 

 area. 



In a considerable number of other places 

 these quartzites have been noted and as a 

 rule they have shown a pronounced banded, 

 if not bedded, structure and have almost 

 always exhibited graphite. They likewise 

 very commonly contain dark, rounded discs 

 of a mineral that proves when examined in 

 thin section, to be monoclinic pyroxene. 

 It is irregular in outline and pale green in 

 color. The rocks are therefore aggregates- 

 of quartz in excess and pyroxene in consid- 

 erable amount and are to be interpreted as 

 old quartz sandstones, that contained some 

 calcareous and magnesian admixture, which, 

 during metamorphism, yielded the pyrox- 

 ene. A little iron oxide also entered into 

 the result. In several instances we have 

 found small masses of the quartzites in the 

 anorthosites, forming inclusions which have 

 been torn off during the intrusion of the ig- 

 neous rock, and which have been surrounded 

 by small zones or reaction rims, due to con- 

 tact metamorphism. 



Minor Associates of the Limestones. — Another 

 peculiar and characteristic rock that is as- 

 sociated with the limestones in many places 

 in minor amounts consists of quartz and 

 milk-white plagioclase, with occasional 



