524 F. G. CLArP GLACIAL PERIOD IN NEW ENGLAND 



PRINCIPAL TILL DEPOSIT (MONTAVK) 



General description. — The principal till deposit of New England in- 

 cludes a large part of the drift which has hitherto been called Wisconsin. 

 It is in most places a very hard blue boulder-clay containing many 

 striated and angular stones and boulders which are in places many feet 

 in diameter. The material is very stiff, and when dug into will stand 

 nearly as well as rock. "When water-worn, as in drumlin sections along 

 the shore, it is eroded into deep gullies, and the shores roimd the base 

 of the section are strewn with boulders. This till ranges in thickness 

 from a few feet to several hundred feet, where it is thickened up into 

 drumlins. The latter are very numerous in Massachusetts and New 

 Hampshire. As a rule, along the coast the till is perceptibly yellow from 

 the effects of oxidation to a depth of 15 to 20 feet from the surface, 

 below wliicli the characteristic unoxidized blue-gray till is found. 



Figure 4. — Wave-cut Section at Little Boars Head, New Hampshire. 



Showing two tiUs and underlying stratified deposit. A, sand and gravel ; B, hard, verti- 

 cal till, Montauk ; C, sandy and bouldery till, Wisconsin. 



Relation to otJier deposits. — The principal till deposit in northeastern 

 New England overlies the Gardiner-Herod clay and gravel wherever 

 these have not been removed by erosion. The till is overlain nearly 

 everywhere in the lowlands by stratified deposits of sands, gravels, and 

 cla3fs of Wisconsin and pre-Wisconsin age. Hence the till is believed to 

 be Montauk. This is the correlation made by Fuller on Long island and 

 cape Cod, and to him belongs the credit of demonstrating the Montauk 

 (possibly Illinoisan) age of the drumlins in the vicinity of Boston.* 



Evidence that this till is not Wisconsin in age. — The evidence that the 

 principal till sheet, hitherto called "Wisconsin," with its drumlins, be- 

 longs in reality to an earlier ice-invasion is fourfold : 



1. It appears to extend from Long island. New York, where its rela- 

 tions are well established and exposed, ahnost continuously to the drum- 

 lins of Boston harbor. 



2. It is overlain by fossiliferous marine clays, which are in turn over- 

 lain by another till deposit (Wisconsin) . 



• Science, new series, vol. 24, 1006, pp. 467-469. 



