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SCIENCE. 



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



4. It forms scattered scales in the rusty- 

 gneisses which are associated with the lime- 

 stones, but here onlj' in comparatively small 

 amount. 



5. It enters richly some pegmatite veins 

 and forms pockets of considerable size as 

 well as ieaf'like individuals which wrap 

 around the component minerals of the rock, 

 penetrate their cracks and impregnate every 

 fissure. In the Ticonderoga veins, which 

 cut across the foliation of a gneiss, the 

 graphite is associated with feldspar, quartz, 

 pyroxene, calcite and apatite, all in very 

 coarsely crystalline development. 



6. It also forms veins by itself in gneisses, 

 as at Split Eock, near Essex, where fissures 

 an inch or more wide are lined with large 

 leaflets, growing out from the walls and 

 mingled with quartz in small amount. To 

 what depth the veins extend cannot be 

 stated, but they run for some yards on the 

 surface in the little prospect where they are 



7. Graphite has been discovered by me in 

 one place in anorthosite, where the latter 

 was in close association with rocks of the 

 limestone series. One or two small scales 

 were detected in the midst of the labradorite 

 crystals. Dr. Hillebrand of the United 

 States Geological Survey has also deter- 

 mined by analysis the presence of carbon 

 not combined as carbonates to an amount 

 of 0.05 per cent, in the igneous, titaniferous 

 magnetites near Lincoln Pond, Elizabeth- 

 town and has obtained traces in samples 

 from two other mines. Gneisses were lo- 

 cated near these intrusions but no lime- 

 stones have been discovered nearer than 

 several miles. 



From the above it is evident that in the 

 cases of the pegmatite veins and included 

 bunches of silicates in the limestones, the 

 carbon of the graphite has been introduced 

 into its present situation in some migratory 

 and penetrating form and that it has per- 

 meated the crevices of the rocks. The in- 



teresting point is whether it has probably 

 come from the intruded magmas, or whether 

 under the metamorphic processes of a re- 

 gional character as well as of a contact 

 nature it has been produced from carbon- 

 aceous matter originally in the sediments. 

 Despite the occurrence of very small 

 amounts in the igneous rocks, my own opin- 

 ion from the preponderating evidence is that 

 it has been derived from the limestones, 

 quartzites and gneisses and has only been 

 worked over, caused to migrate and recrys- 

 tallize by the metamorphosing agents. The 

 practical limitation of the graphite in large 

 amount to the limestones and gneisses seems 

 to me to favor this decision, but I am free 

 to admit that the other view has some points 

 in its favor. There is no question that some 

 conditions, analogous to those which favor 

 the production of pegmatites have been 

 necessary to yield the coarse leaves. Aside, 

 however, from the question of origin, abun- 

 dant experience has proved the value of 

 graphite as an indicator of sediments even 

 if it be not derived from them, and as a sort 

 of ' type fossil ' it is most useful. 



Conclusion. — In conclusion the more im- 

 portant points of our recent work upon the 

 Adirondack sediments may be summarized 

 as follows. They have been shown to be 

 much more widely distributed than we for- 

 merly appreciated, but they are absent 

 from a wide central area, where only mas- 

 sive gneisses and eruptive rocks have thus 

 far been met. That the sediments were 

 extensive is apparent from the evidence 

 and from the thinness of the limestones on 

 the east as well as their association with 

 demonstrable quartzites, we infer that the 

 elastics were deposited in much greater 

 amount than has been realized. Both the 

 nature of many gneisses and also these 

 general considerations lead us to infer that 

 shales or related rocks have been likewise 

 present. On the east at least we have not 

 yet been able to prove that the sediments 



