208 NEW YORK STATE MUSEUM 



Shale is to be avoided, as it breaks up rapidly, forming a sticky 

 mud. 



Gravel, while making a serviceable road, does not pack well, 

 and is not durable. If it has to be used, some of the difficulty 

 may be overcome by cracking the pebbles so as to produce an 

 angular form. 



Clay and Clay Products 



Deposits of clay occur in nearly every county of New York. 

 They belong to three geological periods, namely: 



Quaternary, Tertiary and Cretaceous. 



The clays of the first age are by far the most common. Those 

 of the second are somewhat indefinite in extent, but they prob- 

 ably include a large number of the Long Island deposits. Of 

 the third class there are undoubted representatives on Long Is- 

 land and Staten Island. 



The clays of the mainland are all Quaternary so far as known. 

 The problems of Quaternary geology in New York are by no 

 means solved, and it is not always possible to decide on the 

 causes leading to the deposition of any particular body of clay 

 by a single visit to the locality. 



A great majority of the deposits are local, lying in the bottoms 

 of valleys which are often broad and fertile. They vary in 

 depth from four to 20 or even 50 feet; as a rule they are under- 

 laid by modified drift or by bed rock. The clay is generally of 

 a blue color, the upper few feet being weathered mostly to red 

 or yellow. Stratification is rarely present, but streaks of marl 

 are common. In some of the beds small pebbles, usually of lime- 

 stone, are found, and these have to be separated by special ma- 

 chinery in the process of manufacture. In many instances the 

 clay is covered by a foot or more of peat. 



These basin deposits are no doubt the sites of former ponds 

 or lakes, formed in many instances by the damming up of val- 

 leys, which have been filled later with the sediment of the 

 streams from the retreating ice sheet. The valleys in which 



o Abridged from Bulletin No. 12 New York Stute Museum, by Heinrich Eies. 



