i2 4 CLAYS AND CLAY INDUSTRY. 



GLACIAL CLAYS. 



Origm. — During the Glacial period a mantle of debris of 

 varying- constitution and thickness was spread over the surface 

 by the ice. This deposit, termed till, is commonly very stony and 

 gritty, although containing SO' large a percentage of clayey 

 material that the whole deposit has often been called bowlder 

 clay. Locally, however, it is so free from stones, comparatively 

 speaking, and ;so largely made up of clay that it is used for the 

 manufacture of brick, the few stones being previously either 

 screened out or crushed by grinding. This finer ice-deposited 

 material may be called a glacial clay. 



The streams issuing from the edge of the great ice field which 

 covered northern New Jersey carried vast amounts of rock debris. 

 Most of this was gravel and sand, but a considerable quantity 

 was fine, impalpable rock flour, the finest product of the glacial 

 grinding. This extremely fine material was the last to be de- 

 posited by the streams, since it was the most readily transported, 

 and, for the most, it was carried far out to sea. But, under 

 favorable circumstances, it was deposited in lakes of more or 

 less transient character, near the edge of the ice, or in estuaries 

 which now. by reason of a slow elevation of the land, are 

 wholly or in part above the sea. Wherever deposited by streams, 

 this rock flour gave rise to beds of clay of variable thickness and 

 extent, which may be classed as aquco- glacial clay, since both 

 water and ice were concerned in their formation. Since the 

 glacier covered only the northern part of the State, clays of 

 glacial or aqueo-glacial origin are not to be looked for far south 

 of the line of the terminal moraine, as shown on Plate X, in 

 pocket. 



Clays of the Hackensack valley. — "Beneath the stratified sand 

 and gravel of much- of the Hackensack valley there is a con- 

 siderable body of laminated clay. It is well exposed only about 

 Hackensack, especially in the pits at the brickyards below the 

 city, on the west side of the river, and at a few points in the 

 river bank north of the city. It is known to occur at Riveredge 

 and New Milford, on the Henry Bartch place: is reported to lie 



