GEOLOGY AND GEOGRAPHY OF THE CLAY DEPOSITS. 



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

 They belong to three geological periods, viz.: 



Quaternary, Tertiary and Cretaceous. 



The first class is by far the most common. The second class is 

 somewhat indefinite in extent, but a large number of the Long 

 Island deposits probably belong to it.* Of the third class there 

 are undoubted representatives on Long Island and Staten Island, 

 as well as some additional ones on Long Island, which are 

 questionable. 



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

 The problems of the Quaternary formations 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 and basin-shaped, 

 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 underlain by modified drift or by bed rock. The clay 

 is generally of a blue color, the upper few feet being weathered 

 mostly to red. Stratification is rarely present, but streaks of 

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

 limestone, are found, and these have to be separated by special 

 machinery in the process of manufacture. In many instances 

 the clay is covered by a foot or more of peat. 



The basin-shaped deposits are no doubt the sites of former 

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

 the valleys, and which have been filled later with the sediment 

 of the streams from the retreating ice sheet. The valleys in 

 which these deposits lie are usually broad and shallow. The 

 broad flat valley in which the Genesee River flows from Mt. 

 Morris to Rochester is a good example. The waters of the river 



* F. J. H. Merrill, Geol. of L. I., Ann. N. Y. Acad. Sci., Not., 1884. 



