l6 NEW YORK STATE MUSEUM 



agency of solvent waters, meteoric or magmatic. Among the 

 important occurrences of ores in the Grenville are the zinc-p}T"ite 

 deposits of the Edwards district, St Lawrence county, which have 

 limestone for the walls and are in the nature of replacements formed 

 in Precambrian time. The Grenville schists which are associated 

 more or less closely with the limestone carry extensive bodies of 

 pyrite and pyrrhotite with little or no zinc, but allied to the zinc 

 ores in their method of accumulation. In western St Lawrence 

 county occur small veins of galena with subordinate sphalerite which 

 are of Postcambrian age and probably the work of shallow circula- 

 tions. Hematite in workable bodies is found within the schist and 

 limestone belts of Jefferson and St Lawrence counties. The prin- 

 cipal occurrences are in the belt which extends from near Antwerp 

 in the former county through Gouvemeur into the towns of De Kalb 

 and Canton, St Lawrence county. They occur commonly near the 

 contact of the two formations, but in places are wholly within the 

 schist. They represent secondary deposits formed after Cambrian 

 time; the source of the iron is likely the pyrite-pyrrhotite bodies 

 already referred to. 



Another class of deposits in the Grenville has resulted from meta- 

 morphic agencies by which certain components of the rocks them- 

 selves have been recrystallized or converted into new mineral varieties, 

 so as to acquire economic value. In this class belongs in part at 

 least the Adirondack garnet that is mined for abrasive purposes. 

 There are a nimiber of localities in Essex and Warren counties 

 where garnet of the almandite variety occurs in large quantities and 

 in some places it is apparently the result of r.ecrystallization of 

 calcareous sediments. The occurrences of the type to be seen in 

 the North River Garnet Company's property, however, seem to 

 be referable rather to the absorption of sedimentary material by 

 igneous rocks. The fibrous talc of the Edwards district, which is 

 mined in large quantity, occurs in Grenville limestone; it is an 

 alteration product of tremolite schist produced by silicification of the 

 magnesian limestone under deep-seated conditions. The valuable 

 graphite deposits of Essex, Warren, Washington, Saratoga and St 

 Lawrence counties are found in quartzite and quartz schist of the 

 Grenville series. The carbon content of the sediments is probably 

 original with them, but the influence of heat and pressure has been 

 required to effect its conversion into the valuable crystalline graphite. 



Highlands province. This province includes the igneous and 

 metamorphic terranes of northern Rockland and parts of Orange, 

 Putnam and Westchester counties. The Highlands are a series 



