146 NEW YORK STATE MUSEUM 



dacks. These latter areas are included in a region that has been 

 greatly disturbed, so that the outcrops are not continuous, but are 

 often abruptly terminated by fault lines. Several inlying areas of 

 Potsdam sandstone are also found well within the crystalline area. 



Quarries in Potsdam formation have been opened at Clayton, 

 Chippewa P>ay, Hammond, Redwood, Potsdam, Malone, Bangor, 

 Moira, Keeseville, Port Plenry, Whitehall, Fort Ann and several 

 other localities. 



At present the principal quarries are those of the Potsdam Red 

 Sandstone Co. These quarries are located at the type section of the 

 Potsdam formation, along the Raquette river, 3 miles south of 

 Potsdam. 



The Potsdam sandstone combines great strength and low absorp- 

 tive powers and is thus admirably suited for structural and street 

 work. The rock is typically a hard even grained stone, composed 

 almost wholly of quartz, the component grains being cemented by 

 a secondary deposition of quartz, thus approaching closely to a 

 quartzite. There is enough oxid of iron to give it a reddish color, 

 though in some localities the iron is absent and the rock is nearly 

 a pure white. The Potsdam sandstone has sustained a crushing 

 test of more than 42,000 pounds. 



Hudson River group. This group consists of a great series of 

 sandstones, shales and slates and some conglomerates. The rocks 

 of this group are separated from the Potsdam by the Lower Siluric 

 limestones. The term as here used is an old one and includes beds 

 which range in age from the Middle Trenton to and including the 

 Lorraine beds. As the formations of this group have as yet not 

 been delineated on the map, the group is retained in its former 

 areal significance. 



In southern New York, these rocks are first seen in Orange 

 county, and form about two thirds of the entire area of the county. 

 From here they extend north on both sides of the Hudson river. 

 From Kingston north nearly to Albany they form a narrow belt 

 on the west side of the river, while on the east side they cover a 

 considerably larger area. North from Albany, they are found 

 on both sides of the Hudson as far as Glens Falls and still farther 

 east they extend to the Champlain valley. The greatest expansion 

 of this group is found in the region north from Albany and west 

 of the Hudson. Large porti. ns of Albany and Saratoga and nearly 

 all of Schenectady and Montgomery counties are in this formation. 

 Farther west, except where are southern projections of the crys- 

 talline area, the group extends on both sides of the Mohawk to 



