94 NEW YORK STATE MUSEUM 



described at length in the several areal reports issued by the State 

 Museum. 



The talc deposits are immediately associated with crystalline lime- 

 stones and schists of Grenville age. These occupy belts that have 

 a northeast-southwest trend in conformity with the general struc- 

 tural arrangement throughout the Adirondack^. One of the largest 

 belts begins in the town of Antwerp, Jefferson county, and crosses 

 the towns of Gouverneur and De Kail), St Lawrence county. It is 

 of considerable econo:ric importance in connection with the marble 

 quarries at Gouverneur. A second belt some 12 miles long and 

 from 1 to 3 miles wide is found a few miles to the east in the 

 towns of Fowler and Edwards. It is this area that contains the 

 fibrous talc deposits. A third belt to the south and east of the 

 latter and lying across the St Lawrence-Lewis county line includes 

 the Natural Bridge talc occurrence that has been recently under 

 development. 



The limestones are bordered by members of the Adirondack 

 gneisses, some of which are light in color and have the composition 

 and appearance of slightly modified granites and diorites. A very 

 prominent member in the stretch between Gouverneur and the talc 

 district is a dark hornblende variety which is usually well lamin- 

 ated and garnetiferous and is injected by light red granite. In 

 places the granite forms a branching network that incloses the 

 darker rock in its meshes, producing a mosaic pattern. These 

 granite injections are no doubt offshoots of some of the larger 

 bodies of that rock, while the darker gneiss may belong to the 

 sedimentary series. Of the general relations of the gneiss group 

 it can be said that the igneous types are apparently the youngest 

 and are all later than the limestones. It is not clearly demonstrated 

 as yet whether any of the gneisses in the region are older than the 

 Grenville. 



Occurrence of the talc. The talc deposits occur along minor belts 

 within the Grenville limestones and schists. They are locally called 

 veins and have been described as such by some writers, though they 

 have nothing in common with mineral veins, being layers or beds 

 included within the limestones. They have the same strike and 

 dip as the latter and show a fair degree of regularity and persis- 

 tence. In thickness they range from seams of a few inches up to 50 

 feet or more. The dip is uniformly toward the northwest at angles 

 that vary usually between the limits of 30 and 6o°. 



The associated schists are mainly composed of tremolite, but in 

 some places carry considerable quartz. They are singularly free 



