344 CLAYS AND CLAY INDUSTRY. 



foot of steep slopes or in swampy depressions. They are there- 

 fore glacial or colluvial clays (pp. 7, 13, 120, 124). Those from 

 the southern part of the State were deposited in sheltered bays or 

 estuaries 1 when the land stood somewhat lower in respect to sea 

 level than at present. They were not, however, all formed simul- 

 taneously since there are known to have been at least two periods 

 of submergence during the Pleistocene, and some of the clays 

 belong to the earlier or Pensauken and others to the later or Cape 

 May (pp. 1 30135). Included in this group are also the clay 

 loams (p. 121), which are so widely distributed at levels below 

 240 feet, and which are believed to belong to the closing stages 

 of the Cape May submergence. 



Both groups of clays are commonly of local occurrence and 

 show a variable depth. They are for the most part shallow, but 

 those of northern New Jersey occurring in the basin of the extinct 

 Lake Passaic and along the Hackensack river attain very con- 

 siderable thicknesses, 50 feet being reported for the depth near 

 Hackensack, and still greater depths for the clays in Lake Passaic. 

 In the southern portion of the State the thickness is never great. 

 It varies commonly from 2 to 5 feet around Trenton, and 4 to 

 6 feet in southeastern New Jersey, although south of Bridgeton 

 (Loc. 190), a section of at least 8 feet of clay was seen, and at 

 Belle Plain 7 feet of clay is said to- occur; at Buckshutem (Loc. 

 180), 9 feet of clay is found, but only the upper 6 feet are dug. 

 The overburden rarely exceeds 2 to 3 feet, and may be sandy loam, 

 or gravelly loam. 



The extreme shallowness of the deposits around Trenton (PI. 

 XV, Fig - . 1 ) , has necessitated digging over large areas, in order 

 to keep up a sufficient supply. 



As can be seen from what has been stated above the two groups 

 of clays occur in more or less separated areas. More than this 

 they are rather distinct in their physical properties, those of the 

 first group being invariably red burning, sometimes fine grained 

 and of low fusibility, while those of the second group are pre- 

 dominatingly gritty, and of higher fusing point. 



1 The clay from Hobart's pit, north of Vineland (Loc. 184), is, perhaps, an 

 exception, as it may be due to surface wash. 



