770 A. C. V BATCH 



in the same region have fully confirmed the conclusions from 

 the samples of the Brooklyn water works' test borings. The 

 gravels have a maximum thickness of more than lOO feet near 

 the axis of the old valley, but thin out rapidly in passing east- 

 ward, the last wells in which they are known to occur being at 

 Barnums Island and Long Beach. Farther east, the south shore, 

 protected as it was by the Cretaceous upland, received none of 

 these glacial gravels, but still farther east they again appear at 

 Riverhead, here likewise overlain by clay beds. The local name 

 proposed for these beds is from the Jameco pumping station of 

 the Brooklyn water works, which is a few miles south of Jamaica, 

 New York. . It was here that borings first revealed these beds. 



Blue clay {^Sankaty) . — Overlying these gravels on the south 

 shore are dark-colored clays, having a normal thickness of about 

 50 feet, and containing considerable lignite and occasional frag- 

 ments of shells. These beds were laid down as a marginal coast 

 deposit around the nucleus of older material when the land stood 

 about 50 feet higher than today. On the north shore, where 

 erosion has been more active, these beds exist, at present, only 

 as remnants, associated with somewhat similar Cretaceous clays, 

 and, except where brought up by folding, always below sea level. 

 Their differentiation in well sections and small outcrops is, 

 therefore, neither satisfactory nor certain. In no place on the 

 north shore have sections been seen in which this clay bed and 

 the older gravel are clearly shown ^ — ^a result not to be won- 

 dered at when the fragmentary and folded character of these 

 exposures is considered. In the southernmost of the sand pits, 

 just northeast of Plum Point, near Port Washington, beds of 

 laminated gray clay of probable Pleistocene age are exposed 

 in slightly overturned folds. These may be of the Sankaty 

 age. 



The greatest thickness of this clay in the Brooklyn water 

 works test borings, 150 feet, is believed to be greater than the 

 true thickness of the deposits of this period. The clay bed is 

 perhaps divisible, the portion below a more or less well-defined 

 sand and fine gravel bed, which separates the section when the 

 clay is of considerable thickness, belonging to the last outwash 



