58 GLACIAL GEAVELS OP MAINE. 



SUMMARY. 



Marine erosion of the till and solid rock contributed bnt a small por- 

 tion of the marme sands and clays of Maine The lower marine beds of 

 Maine are clays and very fine sands which are prevailingly fossiliferous. 

 The npjjer clays are rarely fossiliferous, and appear to be contemporaneous, 

 or nearly so, with the basal clay of the valley drift. Overlying the clay 

 of the valley drift is a stratum of coarse matter, which changes to sand near 

 the old shore line of the sea, and then extends for some distance seaward 

 as a fluviatile, not a glacial, delta. The facts indicate that the lower clays 

 are chiefly the finer sediments of glacial streams. The supply of sediment 

 was at that time moderate,, and marine life flourished. Later there was a 

 great rush of glacial waters, and about the same time the ordinary streams 

 began to flow. These conditions were unfavorable to marine life. Still 

 later the sediments poured into the sea were almost wholly those brovight 

 by the present rivers, then swollen to great size. The sands last to be 

 deposited border the river valleys and are plainly deltas formed in the sea 

 off' the mouths of the rivers. The earlier clays are more widely spread, 

 and cover the whole area submerged by the sea, and their thickness bears a 

 relation to the systems of glacial gravel rather than to the modern rivers. 



The distribution of the marine beds is approximately shown in the 

 accompanying map, PI. II. 



VALLEY DRIFT. 



The mass of unconsolidated sediments which is found covering the 

 bottoms of most of the New England valleys early attracted the attention 

 of geologists. Various names have been given to it, the most common 

 being terraces, valley terraces, and valley drift or alluvium. All agree that 

 the material was transported to its present position by water, though some- 

 times it has been referred to marine rather than fluviatile action. The 

 so-called "intervals" of the Maine streams are almost always plains of 

 aqueous sediment, which are usually terraced. Elsewhere are given brief 

 descriptions of the alluvium of the larger valleys of the State. A general 

 discussion of this deposit is therefore postponed to a subsequent page. At 

 present the attention of the reader is called to the more important facts. 



Perhaps the most important fact regarding the sedimentary drift of the 



