144 NEW YORK STATE MUSEUM 



is quarried at Middle Granville and vicinity, and broadening 

 out southward, extends nearly across the (southern part of 

 Rensselaer county. 



Acadian 



The Middle Cambrian, or Acadian, group is not so well de- 

 veloped in New York. 



Marble and limestone of this age are found resting conform- 

 ably upon the Lower Cambrian rocks about Stissing mountain, 

 shown in the cut for the N. Y. & Mas®. R. E. near Stissing, and 

 extending into Massachusetts, where the development is greater. 

 A portion of the Stockbridge limestone may belong to this group, 

 though most of it is Lower Silurian. 



Potsdam 



The Upper Cambrian, or Potsdam, group is exposed over a 

 larger area in New York than the two lower divisions and is 

 typically represented by the Potsdam sandstone, which is seen 

 in many places to rest directly upon the Archaean. It is a hard 

 silicious sandstone and an excellent building material, often 

 thinly bedded and usually reddish-brown in color, though some- 

 times gray or buff. On many of its layers, are waved surfaces, 

 precisely resembling the ripple-marks seen on sandy bottoms 

 over which waters are agitated by waves or currents. They were 

 formed in the same way, by movements of the waters in which 

 were deposited the sands which were finally hardened into the 

 Potsdam sandstone. Similar markings are frequent on almost 

 all sandstones. The edge of this formation can be traced nearly 

 all around the region of the Adirondacks, except between Cana- 

 joharie and Carthage, and is especially well seen near Keese- 

 ville in Clinton county, where the deep chasm of the Ausable 

 river is cut through it, showing 333 ft. of horizontal strata, at 

 Chateaugay chasm, where the section exposes a thickness of 

 250 ft., and at Potsdam, St Lawrence county, from which place 

 it received its name, and where, in the valley of the Raquette 

 river a thickness of 70 ft. is shown. 



