528 F. G. CLAPP GLACIAL PERIOD IN NEW ENGLAND 



a time interval between the deposition of the gravels and that of the 

 overlying clay is found partly in an apparent unconformity at the top of 

 tlie gravels. In the Kennebec valley they rise in places as high as 150 

 feet above tide. In neighboring sections they are absent. The marine 

 clay, which is the next succeeding deposit, in places, as at Gardiner, 

 Augusta, Waterville, and vicinity, rests on top of the higher remnants of 

 gravel, and elsewhere it fills gullies down nearly to sealevel. The objec- 

 tion might 1)6 raised that we have no evidence against the gravels having 

 been deposited "like kames with uneven surface and sporadic distrilm- 

 tion." While the extent of present knowledge in specific localities is not 

 sufficient to prove positively that such is not the case, the general distri- 

 bution of the gravels with rather uniform upper level renders the kame 

 hypothesis rather weak. Even if true, it would not materially affect the 

 general proposition of a time interval, as the change of conditions from 

 those necessary for kame formation and those favorable to deposition of 

 widespread well-stratified fossiliferous marine clays necessitate a more 

 than local ice-retreat. 



2. Occurrence of till overlying the gravels. — One of the best exposures 

 of till overlying stratified sand, clay, and, gravel is to be seen on the 

 southern edge of the village of Augusta, Maine. There are a number of 

 good exposures in gravel pits at this place, which appear to throw light 

 on the succession of events after the deposition of the gravel. Plate 58, 

 figure 1, shows a section where coarse semi-stratified gravel of unknown 

 thickness is overlain by 15 feet of clay and fine sand, folded at a high 

 angle. These deposits are cut off' squarely at the top, as if planed off l)y 

 ice, and are overlain uneonformably by 2 to 6 feet of till. 



3. Erosion and folding of gravels by overriding ice. — This erosion was 

 accompanied by severe folding, as illustrated in a pit a few hundred feet 

 from the last (see plate 58, figure 2). The illustrations show that the 

 folding took place after deposition of the clay (B), and that at the same 

 or a subsequent date there was erosion with the deposition of till (Wis- 

 consin). Other sections in the vicinity show the clay (B) increasing to 

 as much as 30 feet in thickness and forming part of the main marine clay 

 deposit of the valley.* The lower 5 feet of the clay is, as a rule, very 

 sand}', as in figure 1. The shoving illustrated in this plate took place 

 from the north, at the right hand end of the section. 



FOSSILIFEROUS MARINE CLAYS {"LED A CLAY") 



Use of term "Leda clay." — The name "Leda clay" was applied in 1857 

 by Dawson to the fossiliferous marine clays at Montreal,! from Leda 



* A. S. Packard : Mem. Boston Soc. Nat. Hist., 1865," p. 243. 



t J. W. Dawson : On the newer Pliocene and tlae post-Pliocene of the vicinity of Mon- 

 treal. Canadian Naturalist. 1857. 



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