390 GLACIAL GRAVELS OF MAINE. 



the south the intervals become on the average longer and the ridges shorter, 

 till the latter are reduced to cones, domes, and short ridges or plains. The 

 deposits continue to become smaller, and the systems end north of the aver- 

 age line of the coast, and most of them only a few feet above it. 



3. The maximum development of the glacial sediments is found near 

 the contour of 230 feet. 



4. The gravel deposits of the coast region usually have rather gentle 

 lateral slopes and convex summits, and as a class they may be referred to 

 the lenticular type of eskers. 



5. The other characteristics of the coast gravels, their topographical 

 relations, etc., do not differ materially from those of the interior, except that 

 in certain places the gravels of the discontinuous systems or the discon- 

 tinuous portions of the osars and osar-plains have the marked characteristic 

 of appearing on the tops of low hills (less than 120 feet high), while in the 

 intervening valleys gravels are seldom found. 



The above-named facts present special difficulties of interpretation. It 

 is certain that some of the gravels were deposited in the open sea, others in 

 ice channels, but we have to determine, if possible, whether the latter were 

 deposited beneath sea level. Observations made on the land can give us little 

 help in studying offshore deposits; and we are haunted in our investigation 

 by the uncertainties attending the determination of the border line of the 

 ntive. We are able to point out certain agencies that nmst have been 

 engaged in the work, but a satisfactory explanation demands a quantitative 

 estimate of their relative efficiency. This field of investigation is untrod- 

 den as the n^ve of the ice-sheet itself, and my views have not infrequently 

 changed while studying the subject. It seems impossible to take up these 

 questions at any point without anticipating later discussions. 



RETREATAL PHENOMENA. 



A topic germane to a comparison of the discontinuous coastal gravels 

 with those of the interior of the State pertains to the manner of retreat of 

 the ice over a country so diversified by hills and valleys as Maine at a time 

 when a considerable part of the State lay beneath sea-level. Thus, if the 

 terminal melting was either more or less rapid where the ice was in contact 

 with the salt water than where it was above the sea, the retreatal phenomena 

 would be very complex. The ice of the drainage basins of many of the 



