144 NEW YORK STATE MUSEUM 



The change of organic carbon to crystalline graphite has been 

 affected by the heat and pressure accompanying mountain-making 

 stresses, or static metamorphism, causing the volatilization of 

 hydrogen and nitrogen, and the dehydration of the residue, followed 

 be the recrystallization of amorphous carbon to graphite. 1 



The sedimentary limestone type. When discussing the northern 

 area with its characteristic type of graphite, emphasis was purposely 

 laid upon the contact type. While the majority of the prospects 

 and mines are situated at contact zones, some of the limestone 

 appears to be graphitic without any necessary connection with 

 igneous rocks. The limestone, for example, throughout the Paradox 

 Lake quadrangle was frequently observed to be slightly graphitic. 

 The most plausible origin for the graphite in this rock is that it is 

 organic. It may be that the history of the carbon here has been 

 very similar, if not identical with the formation of the Dixon 

 schist. It is a striking thing that as we pass into the interior of 

 the Adirondack highland the limestones become barren of graphite. 

 Whether this is due to the action of igneous rocks culminating in 

 the great anorthosite body or due to the fact that we are moving 

 away from the old Grenville shore into areas where deep-water 

 conditions prevailed, is, of course, unknown. 



THE INORGANIC TYPE OF GRAPHITE 



The contact form. Graphite occurs at contact zones between an 

 igneous rock and a sedimentary one, usually in contact rocks rich in 

 pyroxenes, and in the margins of the eruptive rock. The statement 

 that graphite occurs in pegmatites is probably true per se, but it 

 seems to the writer to be somewhat misleading; for it is confined 

 to the margin along the line of contact. Apparently the country 

 rock was a necessary reagent in the formation of the graphite. 

 Several specimens collected on Lead hill were first taken to be lime- 

 stone with graphite. The trial with a knife blade proved that the 

 white material was too hard for calcite, hence it was called pegmatite 

 material. A thin section showed it was white pyroxene; hence it 

 was a contact rock, not a pegmatite. 



There are two views in regard to the origin of the contact form 

 of graphite: (i) that the carbon, in some form, was an original 

 constituent of igneous magmas, or (2) that the igneous rock in its 



1 See Hatch, F. H. & Rastall, R. H., " Petrology of the Sedimentary Rocks," 

 London, 1913, p. 293. 



