REVIEWS 547 



Local basin-shaped deposits of Quaternary clays occur at many points in the 

 centra], western and southwestern portions of the state. These deposits are doubtless 

 on the sites of former ponds, formed commonly by the damming of valleys, and 

 later filled with the sediment of streams from the retreating ice sheet. A number of 

 these deposits are of economic importance, and some are now worked. 



The most important and extensive clay deposits in the state, however, are those 

 in the Hudson valley. The Quaternary deposits here are of two types (i) estuary 

 deposits of fine stratified sand and blue and yellow clays; (2) cross bedded delta 

 deposits of coarser material. The clay is usually blue, weathered yellow where 

 exposed. It is markedly stratified horizontally, the layers of clay being separated by 

 extremely thin laminse of sand. At many localities the clay is overlain by the delta 

 deposits of rivers tributary to the Hudson. The Quaternary history of the region is 

 summed up as follows : During the retreat of the ice sheet from the Hudson valley 

 the glacial streams deposited as kames a great amount of ground up material, princi- 

 pally shale. Subsequent to the retreat there was a depression of the land amounting to 

 80 feet at New York city and 360 feet near Schenectady. During this depression a 

 great amount of plastic clay was deposited, produced by glacial attrition of shales and 

 limestones. The upper portion of the clay is more siliceous, and it is overlain by an 

 extensive deposit of sand, indicating a change in the nature of the material washed 

 into the estuary. During the period of submergence much of the siliceous matter 

 washed into the estuary was deposited at the mouths of tributary streams to form 

 deltas. 



The clays of the Champlain valley are estuary deposits of the same age as the 

 Hudson river clays. They underlie terraces bordering Lake Champlain, and now 

 standing at an elevation of 393' A. T. Extension erosion has removed much of the 

 clays and sands, and it is only at sheltered points that the terraces are now prominent. 

 The clays are worked for brick at Plattsburg and other localities. 



Cretaceous clays occur on Staten Island, and have been worked extensively at 

 Kreischerville and other points, the material being used in the manufacture of fire- 

 brick, etc. 



1 " There is still some doubt as to the exact conditions under which the beds of clay 

 and gravel which form the greater portion of Long Island were deposited, but it is 

 probable that the clays represent shallow water marine deposits of Cretaceous and 

 Tertiary age .... The age of the clays is still largely a matter of speculation, and 

 will probably remain so in many cases unless paleontologic evidence is forthcoming. 

 Those on Gardiner's Island are quite recent, as shown by the contained fossils, and 

 the clay on Little Neck is Cretaceous. The proof of the age of the Glen Cove clay is 

 not absolute .... The clays at Center Island, West Neck, Fresh Pond, and Fish- 

 er's Island are very similar in appearance and composition, and are very probably of 

 the same age, possibly Tertiary, but we lack paleontologic or stratigraphic evidence. 

 At West Neck, the clay underlies the yellow gravel and the latter is covered by the 

 drift, so that is pre Pleistocene." 



Shales occur in New York in the Hudson River, Medina, Clinton, Niagara, Salina, 

 Hamilton, Portage and Chemung groups. Of these, the last three are the most 



1 In regard to the Long Island clays the author has been quoted verbatim, as the 

 statements could not well be summarized, — E. C. E. 



