1-j- 2 NEW YORK STATE MUSEUM 



limestones [the Faxon limestone] ; (5) in the fairly even dissemi- 

 nation of the graphite through the workable schist." He further 

 supports these arguments by a chemical study of the schist. 1 All 

 of this evidence can be summed up in a few words : The Dixon 

 schist is a stratigraphic unit in a sedimentary series. Having 

 settled to his satisfaction that the schist is sedimentary, Bastin 

 concludes, and the writer feels quite correctly, that this graphite 

 is organic in origin. 



But the graphite, as such, was not present in the original clastic 

 sediments when they were deposited in the Grenville sea. Graphite 

 in unmetamorphosed sediments is known 2 but such occurrences are 

 rare and without much question the graphite has been derived from 

 preexisting metamorphic rocks which have suffered disintegration. 

 We can dismiss this factor as unimportant in the formation of the 

 Dixon schist. 



Walcott 3 has suggested that the Dixon is a metamorphosed coal 

 seam. There are several serious objections to such an interpreta- 

 tion. (1) The metamorphism of a coal bed usually gives a true 

 amorphous or microcrystalline form of carbon; (2) from our 

 present knowledge of coal it would seem improbable that a suf- 

 ficiently developed form of life had appeared in Grenville time to 

 'have furnished coal. 



Kemp's view is that the original rock was a bituminous shale. 

 If we use the term shale loosely, chiefly as signifying a structure, 

 then there is no difficulty in accepting this view, but if an argillaceous 

 sediment is implied then this can be criticized on the ground that 

 the Dixon schist is not a metashale but a metasandstone. Bastin 

 maintains that " it seems most probable that the deposits represent 

 carbonaceous sandstones, locally clayey, interbedded with only 

 slightly carbonaceous impure sandstones and with small amounts 

 of limestone, all of which have been completely recrystallized with 

 the development of a schistose structure and the conversion of the 

 original carbonaceous material into graphite through the usual pro- 

 cesses of dynamic metamorphism." 4 There is some objection to 

 Bastin's term " carbonaceous." True carbonaceous matter in black 

 muds seems to have been derived from ligneous material. Plants 



1 See Bastin, E. S., " Chemical Composition as a Criterion in Identifying 

 Metamorphosed Sediments." Jour. Geol., 17:445. 



2 In Cambrian sandstone, as reported by E. T. Wherry, Econ. Geol., 7:764, 

 and in Triassic Sandstone of Massachusetts, Emerson. Mon. XXIX, U. S. G. S., 



P- 365- 



3 Walcott, C. W., Bui. Geol. Soc. Am., 10:227; U. S. G. S. Bui. 86, p. 398. 



4 Bastin, E. S., Econ. Geol., 5:134, et sec. 



