40 NEW YORK STATE MUSEUM 



Adirondacks, especially the latter series, which the writer regards as 

 of Algoman age, were capable of producing graphite upon contact 

 (metasomatic metamorphism) with nearly all kinds of meta- 

 morphosed sediments. 



That graphite is not always developed at the line of contact 

 between an igneous and a sedimentary rock is, of course, easily 

 observed. The question as to why we find graphite at one place 

 and not at another is not as yet answered to our satisfaction. Some 

 discussion of this problem will be found when we come to the 

 question of the origin of graphite. 



THE GRAPHITE DEPOSITS OF THE SOUTHERN AREA 



In describing the occurrences of graphite in the northern area, 

 where the contact type is best shown, geological details have pur- 

 posely been avoided, but are, however, indispensable in treating 

 the major deposits in the southern area. 



The blanket or bedded form of ore body should be regarded as a 

 distinct stratum of the old sedimentary rocks known as the Gren- 

 ville series. This series represents a succession of marine deposits 

 consisting of limetones, sandstones, shales, conglomerates and their 

 intermediaries that have subsequently been folded, faulted and acted 

 upon by earth forces of such magnitude that their original characters, 

 mineralogical make-up and structures have been greatly changed. 

 The ancient limestones have been recrystallized to white marbles ; 

 the sandstones to quartzites and quartz schists, and the shales and 

 conglomerates to various schists and gneisses. The rocks that com- 

 posed this great series, one of the most ancient known in the 

 world, occur throughout the Adirondacks, but are found more 

 extensively on the flanks of the mountains, such as in the eastern 

 foothills. 



Usually the subdivision of the Grenville into distinct beds or 

 strata has not been attempted in mapping a quadrangle. It is, 

 however, of great practical importance to graphite interests to know 

 the succession (stratigraphy) of the Grenville rocks at the various 

 properties. As the beds exposed in a given locality may represent 

 a portion near the top or bottom of the original series, a district 

 some distance away may expose a different portion; the order of 

 the beds may differ in the two cases. There may also have been 

 horizontal differences due to local conditions of sedimentation or 

 in the degree of subsequent alteration (metamorphism), producing 

 a different kind of rock although representing the same stratum. 



