118 CHAMFLMN DIVISION. 



// i to distinguish the Potsdam sandstone. To distinguish iliis rock from other sand- 

 stones, its position must firsl be noted. Traced downwards, we arc led directly to the 

 primai \ mass, as gneiss and granite ; traced upwards, we find il terminating in a sandy 



limestone. The exception to tins rule is only found in the interposition of a mass of black 

 siliceous slate, with obscure vegetable fossils, as at Whitehall and Chazy;. The Medina 

 sandstone, some parts of which resemble the Potsdam, is connected below with another 

 gra\ sandstone, and above with green fragile shales, [f any doubt exists, look for fossils. 

 Of fossils, a single species, a Unguis!, is common at the High bridge at Keeseville, but 

 small and obscure. At French creek, it is larger, but still obscure, in a sandy variety of 

 the rock one and B half or two miles east of l ho village. 



To learn the geographical position of this or any of the New-York rocks, study the map. 

 It will be seen that this rock encircles \ory nearly the (iivat Primary region north of the 

 Mohawk. Let it he observed, however, that it is wanting from near Fort-Ann in Wash- 

 ington count}, south to the Highlands. It is also wanting in the \ alley of the Mohawk. 

 When this is the case, the next rock, the Calciferous, rests upon the Primary, as at Little- 

 falls, and numerous other places in the \alle\ of the Hudson. 



Before dismissing the Potsdam sandstone, it is necessary to call the attention of the 

 reader to a variety of it which occasionally appears in Washington county. It is a tough 

 black or brown mass beneath the calciferous, and varying in thickness from six or ten 

 in more than one hundred feet. It is difficult to describe it : it is sometimes compact 

 and irregularly striped, and unlike any other rock in the New-York system. It some- 

 times resembles hornstonc, and breaks like it into irregular uncouth lumps with sharp 

 angles : hence it is of no value as a flagging or building stone, except for the coarsest 

 stone fences. This mass may be examined at Bald and Toby mountains : I have spoken 

 of it as equivalent to Potsdam sandstone : it may probably with equal propriety be con- 

 sidered as a subordinate bed of the Calciferous sandstone, inasmuch as it is associated with 

 it at the places just mentioned, and is not known to be associated with the potsdam. It 

 is sufficient to consider it as an intermediate mass ; but it is of no consequence, any farther 

 than as it is necessary to he noticed to complete the description of the entire scries. 



i> 2. Calciferous sands-tonic. 



Considered in its totality, this is one of the most heterogeneous rocks in the New- York 

 system. That part which has furnished the name (meaning a sandstone bearing carbonate 

 of lime, or a mixed rock consisting of siliceous or sandy panicles and limestone), is well 

 designated under the descriptive term, and is easily recognized. But there an- several 

 singular compounds embraced under this term ; ami without a brief notice of them, our 

 descrip: ir_\ would lie incomplete. So heterogeneous is this rock, that Mr. Yanuxem, 



of the Second district, applied the term Calciferous group. 



typical rock under this name, is a gray mass with sparkling grains of lime, in which 

 distinct masses of calcareous spar are always imbedded. It is an impure limestone, being 



