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



diverging osars and osar-plains found at North Waterford, also 

 at the southeast angle of Hogback mountain in Montville, and 

 in the valley of Break-neck brook in the northeastern part of 

 Baldwin. In these and other similar cases the most probable 

 interpretation is that the glacial river for some reason changed 

 its course, so that the two lines of gravels were not formed 

 simultaneously. Probably the channel first in use was the one 

 leading over the higher ground. When the lower channel was 

 opened the old one over the hills would gradually be aban- 

 doned. Yet the ice conditions were so far independent of the 

 shape of the ground that it will be unsafe to affirm that the 

 most favorable land-slope would in all cases be the most favor- 

 able route for a glacial river. 



We may have, then, in the course of a single long gravel 

 system, the glacial sediment taking the form of the osar, the 

 osar-plain, and the plain of reticulated kames, also the marine 

 and lake deltas. All are the work of the same glacial river 

 acting under different local conditions. While it is impossible 

 to treat of the more purely theoretical questions in a single 

 paper, yet a few words as to the relations of these different de- 

 posits and their probable origin will be added. 



The first trace we have of the long glacial river is that it 

 deposited the osar. This proves that it flowed in a rather 

 narrow channel — about 300 feet or less in width. All the facts 

 in Maine, as well as those observed by Prof. Dana in the Con- 

 necticut valley, point to a larger and larger flow of water as we 

 near the end of the ice period. This enlarging glacial river 

 gradually broadened its channel, partly by melting of the ice 

 at the sides, and partly by erosion. If the enlargement of the 

 channel took place fast enough to afford passage for the waters, 

 a broad channel was formed in which the level-topped broad 

 osars were deposited But on long, steep down slopes, espe- 

 cially in the granitic regions where the englacial till was very 

 abundant, vast quantities of sediment were swept down the 

 slopes into the valleys and plains. The glacial channels in the 

 valleys were rapidly filled with sediment. This, together with 

 the great increase in the flow of the waters, forced the glacial 

 rivers to form new channels. In other words, since the con- 

 ditions were those of extraordinary sedimentation, there was 

 not time to enlarge a single channel so as to carry off the 

 waters, but large numbers of narrow channels were formed, 

 connected at frequent intervals one with another by transverse 

 channels. In these reticulating channels the reticulated kames 

 were deposited. It should be noted that these remarks apply 

 only to the reticulated kames not closely connected with marine 

 or lacustrine deltas. No doubt the two classes of ridges are 

 often intimately mixed. 



