1. Bowman — Atlantic Preglacial Deposits. 321 



of Cretaceous and Tertiary deposits northward as far as Cape 

 Ann, from the general likeness of the outlines of the shoals of 

 Stellwagen Bank to Cape Cod and the relations of the now 

 submerged valleys.* The suggestion, though a purely analo- 

 gous one, is of great interest in the further exploration of the 

 field concerned. 



Correlation with Similar Deposits to the South. 



The evidence upon which age determinations are attempted 

 is gathered from a close study of the strata themselves and of 

 adjacent areas. The paleontologic evidence secured does not 

 have the specific quality demanded for the purposes of correla- 

 tions, although none of the evidence of this nature negatives 

 the conclusions reached by other evidence. In short, the con- 

 clusions rest upon presumptive evidence and must, therefore, 

 be held as tentative and suggestive only. 



Continuity of Deposits. — At Marshfield, seven miles south 

 of Third Cliff, greensand beds were noted by Hitchcock as 

 early as 1830. f Their age was later determined by Dr. Dall 

 from fossil evidence and found to be Miocene. The deposit 

 is highly glauconitic, occurs about up to 15 feet above mean 

 tide level, and is in very close contact with the granitic floor, 

 which outcrops two miles farther south. The sands do not 

 outcrop, but are reached by excavating 6 to 8 feet beneath the 

 surface. They were first discovered in digging for a well on 

 the farm of Mr. Kent. 



The presence of this bed suggested that coastal sections 

 between Third Cliff and Martha's Vineyard might show similar 

 deposits, but a search from Boston Harbor to Peaked Cliff, 15 

 miles southwest of Plymouth, proved fruitless 'except for the 

 finding of drift material often in great abundance derived 

 from preglacial beds undoubtedly similar to those at Third 

 Cliff. This is particularly true of parts of the glacial deposits 

 at East Marshfield, Kingston, Indian Hill, Lookout Point, and 

 Peaked Hill. The unusual character of some of the glacial 

 material in these places is very striking. There is a large 

 amount of white and red sand rather poorly mixed with the 

 more common brown sand noted in sections of glacial mate- 

 rial farther inland. These suggest the wider extent of the pre- 

 glacial deposits and their considerable erosion by ice. 



Similarity of materials. — The fact that at least a part of 

 these deposits were formed in relatively shallow water near 

 shore, as shown by the cross-bedded structure of the lower 

 sands, renders their correlation on this ground along with 

 similar deposits on Martha's Vineyard insecure, because of 



* See map of the Cape Cod District. 



f £i Final Eeport on the Geology of Massachusetts, " pp. 91-95, and 427 r 

 1841. 



