312 H. T. LITTLE — ^PLEISTOCENE GEOLOGY OF WATERVILLB, MAINE 



suddenness of the change, and the rather homogeneous character of the 

 material bounded by each change. Two explanations at once suggest 

 themselves : first, that the varying de|:)osits represent variations in stream 

 velocity, due to weather changes; and, second, that the variation is due 

 to a sudden accession of water gained through piracy of other water- 

 courses within the ice or the formation of new fissures admitting an 

 increased supply from the surface. The most likely supposition, for the 

 two upper members seems to me to be the simple one of variation in 

 weather. This is borne out by the fact that in many exposures similar 

 beds of finer and coarser gravel alternate, as seen in plate 13, figure 2. 

 New accessions of water by the methods pointed out must also surely have 

 played some part in the variations. 



The lowest of the three members composing the lower gravels, and 

 described as a fine, buff, quartzose sand, is not so easily explained. Its 

 relations are not clearly exposed at any point, but at the best exposure it 

 extends out several yards along the flat to the east of the esker, and also 

 underlies the other deposits of the esker at about the same level. If it 

 were not for the fact that it underlies the other deposits of the esker, it 

 would be natural to look on the sand as a delta deposit in connection with 

 the retreating glacier, or as a lateral deposit in a widened esker channel ; 

 but if that were true, it should grade into the coarser deposits rather than 

 underlie them, with no apparent change of character. It certainly is not 

 a glacial deposit, for it is perfectly sorted and beautifully cross-bedded. 

 Its interpretation is made more difficult by the fact that there is nowhere 

 an exposure showing on what kind of material it rests. Its position is 

 just thati which a preglacial deposit would occupy, such as might be 

 formed in front of the advancing ice-sheet by small streams in a short 

 melting season; but the difficulties in such an explanation — such as the 

 preservation of so loose a deposit — are so great that I would not care to 

 advance this as a probable explanation. 



THE OLDER SANDS AND GLA78 



Overlying the lower sands and gravels is the marine clay formation, 

 often divided into a lower member, the Leda clay, and an upper member, 

 the Saxicava sands. It overlies unconformably the coarse or fine gravels 

 or rests directly on the slate. This unconformity has been considered by 

 some to represent merely the preexistent irregular surface due to drift 

 and fluvio-glacial deposits. There is no question but that the base of the 

 clay would be exceedingly irregular, even though the surface on which it 

 rests had never been subjected to erosion. N'evertheless most of the sec- 

 tions seem to show evidence of further increase of irregularity through 



