532 F. G. CLAPP GLACIAL PERIOD IN NEW ENGLAND 



stood at a much higher level during the deposition of the gravels and sub- 

 sided before the deposition of the clay. 



Another explanation of the unconformity lies in the possibility that 

 the gravels may represent morainal or kame deposits formed under watci 

 between the ice and the valley walls. In either case the subsequent thick 

 deposit of clay filled all the inequalities in the bottom of the valley, result- 

 ing in the unconformity as we find it. 



Correlations. — The "high-level" clays are found to rest in places un- 

 conf ormably on gravel ; in others on tough, stony, clayey till of proliably 

 Montauk age, 'as at York, Maine, and at Uanvers and Cambridge, Massa- 

 chusetts. In a few cases the clays have been seen to rest on rock, Imt as 

 a rule till or gravel intervenes. 



As the clay contains fossils at numerous localities, some of them in 

 close proximity to glaciated boulders, the material must have been depos- 

 ited when the ice-front was still not over a few hundred miles distant. ■ The 

 facts can be accounted for by the supposition that the clays were deposited 

 while the ice-front retreated northward across the states of Maine and 

 New Hampshire, the boulders being transported by icebergs broken off 

 the ice-front in the Kennebec, Androscoggin, Penobscot, and other large 

 valleys. The presence of similar phenomena in the Saint Lawrence 

 valley can be explained by the assumption that the ice remained on the 

 highlands of the interior of New England and of Canada long after the 

 Saint Lawrence valley was free and open to the ocean. 



The marine clays are overlain in places conformably by a few feet of 

 fine sand ("Saxicava sand" of Dawson) (see plate 59, figure 1). In 

 other places they are overlain unconformably by sands. Over wide 

 areas in southern Maine the irregularities are filled and the whole deposit 

 obscured by broad outwash plains of sand sloping seaward. On these 

 sand plains no till is found, but where the clay is not buried by sand it 

 can often be seen to be covered by a heterogeneous gravelly deposit, in 

 places, as at Exeter, New Hampshire, forming small moraines, and be- 

 lieved to be Wisconsin till (pages 536-537). The clay covered by this 

 material is the "high-level clay" of pre-Wisconsin age, Mduich was probably 

 deposited in the Vineyard interval of Woodworth. Being subsequent to 

 the post-Montauk gravels, which have been provisionally correlated with 

 the Illinoisan, the clay would seem to be somewhere near lowan in age. 

 Although very unlike in lithologic character, it has certain aspects in 

 relations and distribution which resemble some of the water-laid types of 

 the lowan loess of the West. 



Evidence that this clay is not of Wisconsin age. — The evidence sup- 

 porting the view that the "high-level" cla}'s are of pro-Wisconsin age is 

 as follows : 



