318 H. r. LITTLE PLEISTOCENE GEOLOGY OF WATERVILLE, MAINE 



drawal of the marine waters cut throngli these clays and perhaps into 

 the "underlying slates. If the slates were reached and eroded, this would 

 account for the irregular thickness of the fluviatile clay. If, on the other 

 hand, the slates were not reached, the clays could be explained as river 

 silts, formed by a meandering stream, which had quickly reduced its bed 

 well toward baselevel in the easily eroded marine clays. The irregular 

 thickness would then be due to the unremoved marine clay beneath, which 

 we have already seen was deposited on a very irregular surface. If glacial 

 groovings could be found in the ledge beneath the terrace, it would be 

 evident that this latter case is the true one ; but I have found no oppor- 

 tunity to apply tliis test. Conditions are said to be more favorable for 

 the formation of mud-cracks under floodplain conditions than estuarine, 

 which bears out the opinion that these deposits are of fluviatile origin. 

 The sands overlying them probably mark the beginning of a new land 

 elevation. The streams were rejuvenated and transported coarser sedi- 

 ment, which they deposited in times of flood on top of the clays. Cer- 

 tainly re-elevation brought about the present condition of active cutting 

 through the clays and many feet into the ledge. 



The Fossils of the Clay 



As already pointed out, certain parts of the marine clay are quite fos- 

 siliferous. The localities where T have found fossils are indicated by 

 riumerals in diagram 1. The altitudes above sealevel where the fossils 

 occur, determined by Y level unless otherwise indicated, are as follows : 



No. Elevation Stratigraphic position of fossils 

 Railroad cut, 1 mile north of 1 139° About 12 feet from top. 



Benton. 

 Cellar foundation, first house 2 135.. 31 Three feet below surface, 

 on Britt street. 



City Gravel Pit 3 123 . 55 Near the base, near the top, and 



138 " in sand immediately overlying. 



Barton's Gravel Pit 4 120.87 About 6 feet above base. 



Lockwood Gravel Pit 5 139 . 81 At very base of clay, even into 



basal conglomerate. 

 Chamberlain's Gravel Pit 6 149° (?) Only one fossil found. 



Of these, the City Gravel Pit has yielded all but one of the species 

 found at the other exposures and many additional ones. For this reason 

 it alone is described in detail. The only thing of special interest in any 

 of the other sections is at locality 5, where the unusually large proportion 



» Determined by aneroid barometer. 

 >o Determined by Loclfe levgl, 



