28 



CAPE COD GEOLOGY 



PHOSPHATIC NODULES IN THE GREENSAND 



In addition to the nodules containing fossil crabs in the greensand bed at 

 Gay Head, there are numerous dark nodules having irregular surfaces, which 

 Lyell spoke of as coprolites. These nodules range in diameter from one to two 



Fig.2 . — Map showing the probable Miocene boundary from Massachusetts southward 

 to Chesapeake Bay. 



inches. An analysis made for Lyell showed that they contain no less than 50 

 per cent of phosphate of lime, together with fluoride of calcium, chloride of 

 sodium, and other constituents. 1 Shaler, for whom a partial analysis of similar 



1 Lyell, Charles, Travels in North America, 1, p. 257, London, 1845. American edition, 1, p. 204, 

 New York, 1845; Shaler, N. S., Report on the geology of Marthas Vineyard, Seventh Ann. Rept. U. S. 

 Geol. Survey, p. 360, 888. 



