456 GLACIAL GRAVELS OF MAINE. 



is always uneven and contains kettlelioles and basins of various depths. 

 Sometimes a few kettlelioles or hollows in what would otherwise be a rather 

 level plain are all the signs of reticulation that we find. Here the ridges 

 are so broad and plain-like as to obscure their origin as reticulated ridges. 

 Where the reticulated ridges are best developed there is a pretty regular 

 gradation in the forms of the ridges. At the landward side of the delta, 

 usually the north and northwest, the gravel is coarse and the ridges are 

 high and have rather steep lateral slopes. The basins are correspondingly 

 deep, and the transverse ridges are well defined. As we go away from the 

 place where the mouths of the glacial rivers were the ridges become 

 broader, though still with arched cross section. Soon the ridges are so 

 broad as to be plain-like, and so nearly coalesce that the kettleholes are 

 only shallow hollows, and there is a gently undulating plain of fine gravel- 

 When the area of sand is reached, the plain becomes nearly level on top 

 and shows hardly a trace of separate ridges. The stratification is here 

 nearly horizontal, and so continues into the region of clays, where all signs 

 of the separate ridges are lost. The broad osars sometimes pass into marine 

 deltas by only a few reticulations (as in New Gloucester; see pp. 227-228). 



1. The existence of glacial potholes and the phenomena of the non- 

 continuous gravels prove that subglacial streams existed in the coastal 

 region, and that they were concerned in osar formation, as has previously 

 been pointed out. 



2. But glacial marine deltas occur in the course of the osars as a reg- 

 ular part of their development, sometimes more than once in the course 

 of a single river. They mark epochs in the history of the osar rivers, 

 showing where the ice front stood at particular epochs. They are thus 

 retreatal phenomena, not changing the character of the rivers in any way, 

 but merely .the conditions of sedimentation. If the discontinuous gravels 

 were deposited by the subglacial rivers, so were the marine deltas. Here 

 there can be no compromise between the rival subglacial and superglacial 

 hypotheses. Superglacial streams must account for all the coastal phe- 

 nomena, including the deltas, noncontinuity of deposition, decrease in 

 quantity toward the south, the petering out of the streams near the northern 

 ends of the "rivers" or fiords of the coast, the lenticular shape of the 

 gravel masses, the underlying terminal moraines, etc., or they must be 

 ruled out of the coastal region altogether, except in the subsidiary form of 



