120 CLAYS AND CLAY INDUSTRY. 



POST-PLEISTOCENE CEAYS. 



Character. — The clay deposits which are to^ be considered as 

 belonging- to< the post-Pleistocene or recent period 1 are small, im- 

 pure and of local importance only. 



Along some of the streams shallow beds of sandy and often 

 stony clay occur on the flood plains, i. e., those areas subject to 

 overflow in times of high water. They are clearly the result of 

 the deposition by the stream of the finest material it carries in 

 time of flood. Elsewhere swamps and marshes are underlain by 

 clay, which has resulted from the fine mud washed into them by 

 rain and streams. This clay is usually more or less sandy and 

 often contains a large amount of vegetable matter. In still 

 other localities of the State beds of sandy or stony clay have 

 accumulated at the foot of slopes, as the result of the wash, by 

 rain water, of the finest material from the hills above. Since in 

 such locations there has been very little mixing of the material, 

 these deposits often resemble closely the residual clay formed by 

 the decay of rock in place. All these clays are usually either of 

 a mottled yellow or red color, due to 1 iron staining' or black, as 

 a result of the large amount of vegetable matter contained in 

 them. They are of limited extent, both in area and thickness, 

 and are rarely of any value save for the manufacture of com- 

 mon brick. For this purpose, however, they often serve admir- 

 ably and afford workable clay for small brickyards supplying a 

 local demand. Owing to> the diverse ways in which these de- 

 posits originate, the clay varies considerably in character and 

 the value of each deposit has to be judged separately. 



Localities. — Clay of this nature is used at several localities in 

 New Jersey. At Dunellen (235), 2 Rajotte's clay pits are located 

 along the swampy flood plain of Green brook. The clay is 4 to 

 6 feet thick, covers at least 14 acres, and is underlain by gravel 

 of late Glacial age. The clay is evidently a swamp and flood 

 plain accumulation of post-Glacial or recent time. 



1 It is not possible to estimate accurately geological periods in years, but 

 their length is to be calculated in thousands rather than hundreds of years. 



2 These numbers all refer to localities shown on Plates X, XI, XII, XIII. 



