54 NEW YORK STATE MUSEUM 



are today and greatly reducing the inequalities of contour. The 

 waste thus derived was washed toward the sea to form the first 

 of the normal fossiliferous rocks. 



The Paleozoic era began with the deposition of sediments upon the 

 uneven surface of the Precambric crystalline rocks. It appears that 

 with the close of the Precambric era the land which had remained 

 above water since Grenville time underwent a gradual subsidence, 

 bringing the outer borders within reach of the sea. With its sub- 

 mergence there were formed stratified deposits which contain the 

 earliest records of life that are at all well defined and abundant. 

 The lowest members, belonging to the Lower and Middle Cambric 

 groups, are not so widely developed in this State as the Upper or 

 Saratogian group in which lies the Potsdam sandstone. This is 

 exposed in a rather broad but variable belt on the north and north- 

 western sides of the Adirondacks where it still preserves a horizontal 

 position on the eroded edges of the Precambric rocks. It is also 

 present in the Lake Champlain valley and on the southeastern edge 

 of the Adirondacks as broken areas of a once continuous belt. In 

 its characteristic form it is a cjuartzite, and a very hard, durable 

 stone. The lowermost Cambric beds include the Poughquag quartz- 

 ite in southern Dutchess county and the Georgia slates found in 

 the metamorphic area along the New England boundary. Besides 

 the Potsdam cjuartzite, the Saratogian group also contains some 

 limestones of which the better known member, the Little Falls 

 dolomite, is quite extensively developed in the Mohawk valley and 

 is the basis of quarry operations. The limestones are usually im- 

 pure, representing a transition from the sandstones to the high- 

 grade limestones above. 



With the continuance of the submergence and consequent deep- 

 ening of the waters, the deposition of the Champlainic or Lower 

 Siluric beds was begun without any break or interruption to mark 

 the line of division with the Cambric group. The more important 

 representatives in the lower part consist of limestones, of which 

 the Tribes Hill, and Beekmantown and Chazy members may be 

 named. The first has little importance areally, but the Beekman- 

 town (inclusive of the middle and upper beds as earlier defined) is 

 quite widely distributed in the Champlain valley. The Chazy is 

 found in the same region from Saratoga county north to the Cana- 

 dian border ; it is one of the purest calcium limestones in the 

 State. The subsidence of the land surface continued and the waters 

 encroached more and more upon it. This provided opportunity for 

 the deposition of the Mohawkian (Trenton) group of limestones, 



