CAPE COD GEOLOGY 



19 



of Comparative Zoology, and recognized it as a fragment of the skeleton of a 

 Pliocene camel. It, therefore, appears that the osseous conglomerate is made up 

 of a mixture of the bones of marine and land animals that ranged in age from 

 Miocene to earliest Pleistocene and can hardly be regarded as a pre-Pleistocene 

 deposit. An examination of the section in 1916 threw no further light on the 

 question. The boulders of conglomerate in the greensand were either derived 

 from some underlying formation in the Cretaceous system or were thrust into 

 the greensand from above, as boulders are rolled along and sink in soft mud. 



The paleontologic evidence, though scant, is here accepted as sufficient to call 

 for such a revision of the classification of the Miocene and early Pleistocene 

 deposits at Gay Head as will remove the conglomerate and its abundant Miocene 

 fossils to a position at the base of the Pleistocene. 



CHARACTER OF THE DEPOSITS 



The Miocene deposits of this region consist of beds of greensand, most of 

 which are brownish red, weathered, somewhat compacted masses of small grains 

 or nodules, which near the base of the bed, or deeper within the section, become 

 greenish to bright green, the color of typical greensand. The larger grains are 

 between 0.5 mm. and 1.5 mm. in diameter, and many of them show the outlines 

 of the well-known foraminifers of greensand deposits. 1 The presence of these 

 beds in the Miocene series in this part of the Atlantic coastal plain is somewhat 

 anomalous, and W. B. Clark and F. J. H. Merrill have raised the question whether 

 the beds may not have been redeposited from a marine Cretaceous section that 

 was invaded and partly reworked by the advance of the Miocene sea. The Mio- 

 cene age of the greensand bed is indicated by the fossil mollusks and vertebrates 

 it contains. The greensand is relatively pure, but at Gay Head a few rounded, 

 highly polished quartz pebbles are found in the middle of the bed, and near its 

 base there are numerous coarse grains of quartz. The bed of greensand exposed 

 on the southwest side of Nonamesset Island contains a large percentage of coarse 

 rounded quartz grains, 3 to 4 mm. in diameter, literally a fine gravel. 



GASTROLITHS IN THE GREENSAND AT GAY HEAD 



The greensand bed at Gay Head contains scattered, smooth, shining quartz 

 pebbles, the largest li inches long. The high polish of these pebbles and their 

 association with the fossil remains of a supposed seal and a walrus suggest that 



1 Cushman, Joseph Augustine, Some Pliocene and Miocene foraminifera of the coastal plain of the 

 United States, U. S. Geol. Survey Bull. 676, p. 100, 1918. 



