REPRESENTATIVES OF PRE-WISC0NS1N TILL 3 I 5 



deposited between an earlier and a later ice advance. The two 

 tills, however, were identical in character, and presented nothing 

 indicative of any considerable time interval between their depo- 

 sition. The tills and the included stratified drifts are probably 

 to be regarded simply as marking local variations of the same 

 general invasion. Drumlins in which layers of modified drift are 

 inclosed in the till were also mentioned as occurring in other 

 parts of Massachusetts and in New Hampshire and New York. 



The descriptions of the drumlins at Scituate were repeated by 

 Upham in 1894 in his paper on the " Madison Type of Drumlins," 1 

 but no new facts of importance bearing upon glacial conditions 

 in Massachusetts were presented. 



In the table and descriptions accompanying his paper on the 

 clays of Rhode Island and southeastern Massachusetts Wood- 

 worth, 2 in 1 896, gave three glacial epochs. The first and second 

 were separated by the deposition of the fossiliferous marine 

 gravels, sands, and clays of the Sankaty sub-epoch, as was recog- 

 nized by Shaler on Nantucket. The second ice invasion, which is 

 apparently assumed (p. 977) as the cause of the strong folding 

 of the Cretaceous, Tertiary, and early Pleistocene strata of. Gay 

 Head, etc., and the la.st invasion are separated by what is desig- 

 nated as the Vineyard interval of extensive subareal erosion, 

 accompanied by deposition below the present sea level. 



In the chapter on the clays about Boston, Marbut and Wood- 

 worth 3 give reason for believing that the clays were probably of 

 esturine or marine origin, and were deposited in connection with 

 a previous ice invasion. Several sections are described and 

 illustrated which show that the clays are in a number of cases 

 overlain by drumlins which were formed during the last ice 

 advance. The clays frequently present evidences of strong ero- 

 sion, probably due largely to the action of over-riding ice 



1 Am. Geol., Vol. XIV, pp. 69-83. 



2 The Glacial Brick Clays of Rhode Island and Southeastern Massachusetts : The 

 Geology and Geography of the Clays. U. S. Geol. Surv., Seventeenth Ann. Kept., 

 Pt. I, pp. 975-9»S- 



3 Loc. cit., pp. 989-998. 



