Pensauken Formation — Description. 8i 



formation. This member is rarely more than a foot or two 

 thick. (2) The middle member is predominantly of sand. More 

 commonly than otherwise, the sand is arkose and well stratified. 

 It contains little gravel, though pebbles occur singly and in thin 

 beds which appear as bands in sections. Bowlders and cobbles 

 are virtually absent. In thickness, it varies greatly. Where the 

 formation is thickest, this member makes up the larger part of the 

 whole. (3) The uppermost member is gravelly, the gravel being 

 rather fine, with some admixture of loam, and without distinct 

 stratification. This member is thin, in most cases less than 10 

 feet, and in many places not more than 4 or 5 feet. 



This three-fold subdivision can be looked upon as having a 

 general application only. At many points it is not apparent. In 

 many places material corresponding in physical constitution to 

 but two of the three members is present, and the one which 

 appears to be wanting may be any one of the three. Nevertheless 

 the following generalizations seem to be warranted : ( 1 ) that 

 during the earlier part of the Pensauken deposition more coarse 

 material was contributed to the deposit than at any other time, 

 and that of this coarse material a larger percentage was of 

 crystalline rock or shale, than at any later stage of the epoch; 

 (2) that during the middle and probably the greater portion of 

 the epoch, sand, mostly arkose, was the chief constituent of the 

 deposit; and (3) that during the later portion of the epoch, 

 gravel was again more abundant, but gravel in which crystalline 

 rock and shale were almost wanting. The region from Raritan 

 to Raritan Bay was an exception to the last statement above, for 

 here the last phase of the Pensauken appears to have been near 

 the edge of an ice sheet, and in it shale and crystalline material 

 are abundant. 



The middle member is the only one which shows distinct strati- 

 fication persistently. Its individual beds" are in places thin and 

 horizontal, but sharp cross-bedding is almost equally common. 

 Where gravel is associated with the sand, the pebbles are in 

 many cases in thin beds, making lines of pebbles as seen in 

 section. 



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