CLAYS IN TERTIARY FORMATIONS. 145 



THE ASBURY CLAY. 



Stratigraphic relations. — In Burlington and Salem counties the 

 fluffy sand apparently forms the base of the Miocene. In Mon- 

 mouth county, however, the lowest portion of the Miocene con- 

 tains numerous beds of clay underlying- the fluffy sand and grad- 

 ing upward into it by interstratification. Locally, these clay beds 

 attain considerable thickness, and, where not too deeply buried, 

 form deposits of considerable economic importance. From their 

 development just west of Asbury Park, they may be called the 

 Asbury clay. It is believed that these clay beds lie below the 

 great mass of "fluffy sand,'' and, therefore, at a lower horizon 

 than the base of the Miocene farther southwest. In other words, 

 it is believed that the successive Miocene formations overlap 

 each other to the northwest, so that in Burlington, Gloucester, 

 Camden and Salem counties its base, where exposed, lies farther 

 up the dip of the formations than in Monmouth county, and con- 

 sequently the basal beds, as exposed in the former counties, are 

 not so low as those shown in Monmouth county. It is not cer- 

 tainly known whether the Asbury clay forms a single, well- 

 defined bed of wide extent and varying thickness, or whether it 

 is rather a series of overlapping clay lenses, some thin, some thick, 

 separated by beds of fine, loose, light sand, all occupying about 

 the same general horizon. On the whole, the evidence seems most 

 to favor the latter view. 



Occurrence. — Just west of Asbury Park the clay is well ex- 

 posed in Drummond's pits (217), where 12 feet of dark clay, with 

 thin laminae of sand, underlie 8 feet of fluffy sand, with thin clay 

 laminae. Midway in these overlying beds there is a 6-inch layer 

 of fine quartz gravel. The clay continues some depth below the 

 present workings, a 2-foot bed of sand separating the worked 

 from the unworked clay. The top of the clay is about 26 feet 

 A. T., and its base cannot be less than 10 feet, since the under- 

 lying marl is found along the brook just north of the pit. Clay 

 similar in appearance to this, but not so thick, outcrops at in- 

 tervals for half a mile west along Asbury avenue. Its elevation 

 increases westward. At Decker's pits (216), on the N. J. South- 

 10 Ch G 



