142 G. H. Stone — Glacial Sediments of Maine. 



1. The phenomena of the osar-plains prove that not infre- 

 quently broad channels existed within the ice up to a half 

 mile or more in width. Within these channels great rivers 

 deposited plains of nearly horizontally stratified gravel and 

 sand. These are purely glacial sediments. 



2. In numerous instances these broad channels extended 

 across the valleys in which they were situated. In such cases 

 the plains of glacial sediment cover the whole bottom of the 

 valley from one side to the other. They thus occupy the 

 position natural to fluviatile drift and are indistinguishable 

 from it except by tests involving the study of many facts. The 

 osar border-clay is a collateral phenomenon of the same class. 



3. In like manner osars of unmistakably glacial origin 

 expand into plains that soon extend across their valleys after the 

 manner of valley drift. These are the frontal deltas or plains. 



4. In general the alluvium of valleys parallel with the direc- 

 tion of ice flow is considerably coarser in composition than that 

 of valleys transverse to this direction, and the stones are much 

 more water worn. 



5. The larger of the present rivers poured great quantities 

 of sediment into the sea while it stood at the contour of 230 

 feet or thereabout. This apparently was cotemporaneous 

 with the first flow of the rivers in their present valleys, after 

 the ice had become so far melted as to permit them. The 

 coarser fluviatile sediments at that time brought into the sea 

 are now found in the form of broad sheets of sand which 

 extend twenty or more miles south of the contour of 230 feet. 

 These fluviatile sands may be termed fluviatile deltas to dis- 

 tinguish them from the off- shore deposits of the glacial rivers. 

 All of them end before reaching the present shore unless the 

 delta of the Androscoggin be an exception. For example, the 

 Kennebec River of valley drift time poured into the sea in or 

 near Madison and the fluviatile delta-sands of that time form" a 

 sheet one or more miles in width, which overlie the marine 

 fossiliferous clays and extend as far south as Waterville. If 

 during the retreat of the sea to its present level the Kennebec 

 had continued to pour as large quantities of sand into the sea as 

 it did while its mouth stood near 230 feet, we ought now to find 

 a sheet of sand one to three miles wide covering the marine 

 clays all the way southward to the present coast. Instead, we 

 find only a small amount of fluviatile delta- matter south of 

 Waterville, and this forms only a narrow strip near the river 

 and is hardly distinguishable from the present flood-plain of 

 the river. This proves that it was only while the sea stood at 

 or near 230 feet that the swollen rivers of the Yalley Drift 

 epoch were able to transport large amounts of sediment. The 

 shortness of this period is proved by the limited amount of 

 erosion wrought b} 7 the sea. 



