504 VARIATIONS IN THE POTSDAM SANDSTONE. 



slate, and lastly gneiss, are the prevailing rocks, till 

 Washington is reached, and Hinsdall on the summit 

 level. Thence the descent towards the Hudson com 

 mences over the frequently-folded edges of mixed lower 

 silurian limestones and slates, more or less metamorphic. 

 In this border county of Berks, just beyond the summit 

 level, lies the richest agricultural district of Massachusetts. 

 The township of Pittsfield, situated in a beautiful 

 valley, and that of Richmond, form the centre of this 

 district, which is the more interesting to the scientific 

 agriculturist from the circumstance that its geological 

 character at once enables us to predict what in favour 

 able circumstances its agricultural character should be. 



The Potsdam sandstone, until recently considered the 

 lowest of the fossiliferous beds of the United States, is 

 altered in this county, (Berks,) and, indeed, in nearly its 

 whole course south towards the Atlantic, in various degrees, 

 and in a way that is very instructive. In the majority 

 of places it is a hard indurated quartz rock, and is there 

 fore distinguished by the name of the quartz rock by 

 President Hitchcock. In other places it is a very hard 

 and durable sandstone, is especially famous as a firestone, 

 and is transported for the erection of furnaces even as far 

 as Maine. In other places, again, the escarpments of the 

 rock are only loose and crumbly quartz sand, of a dazzling 

 whiteness, and often of exceeding fineness. In these 

 localities it can be dug out from its native bed with the 

 spade and mattock, and possesses the singular property, 

 even when it is excavated in harder lumps, of falling to 

 a fine powder when thrown into water. It has been 

 found by trial to be superior in this powdery state to our 

 English Lynn sand for the manufacture of a colourless 

 glass, and is now dug out, reduced to powder, washed by 

 being thrown into a current of water, and transported to 

 Boston and elsewhere for the use of the glass works. It 

 is delivered at Boston at the price of five dollars a ton. 



