Review of Recent Geological Literature. 137 
feet above the sea there is a maximum development of glacial sediments, 
and that they diminish in amount in opposite directions from this line, 
the gravels in particular becoming more and more discontinuous in ap- 
proaching the coast. 
7. The osars. These are longer two-sided gravel ridges some of 
them extending more than 100 miles northward. At their southern 
extremities, about the level of 230 feet, they break up into non-continu- 
ous kames ( No. 6) and finally disappear in marine deltas. 
8. Broad osars or osar plains. These are simply local expansions of 
the osars (No. 7) into plains due to the widening of the ice valley in 
which the glacial river flowed. Prof. Stone regards the rivers, at these 
places, as having been probably open upward to the sun, but leaves us 
to infer that in general he considers the river that produced the osar 
proper to have been subglacial. These osar plains when later cut down 
by streams show the origin of the terraces composed of glacial sedi- 
ments that accompany so many valleys in New England. 
9. The reticulated kames. This is a "plexus" of ridges, containing 
kettle holes, found at the landward ends of the marine and lacustrine 
deltas. In general they appear to be only a feature of the deltas, but 
some are found unconnected with deltas. They are between 230 and 600 
feet above the present sea level, mostly in rather broad valleys and in 
level regions. They seem to be due to a concentrated action, or to a 
duplicated effect of several glacial streams entering the general valley 
at these points, and also to a gradual shifting of the course of the 
streams near their mouths due to the gradual recession of the ice 
margin. 
10. Osar border-clays. This is a broad-channel deposit of finer ma- 
terials, due to the same conditions and forces. 
11. Frontal plains. These are plains of sediment brought by glacial 
streams down to the extremity of the glacier and then spread subaerially 
over the land in front of the ice. It is hence a "valley drift" of glacial 
date. 
12. Much of the so-called valley drift, or thick sheets of alluvium 
which covers the larger valleys of New England, is not considered as 
the result of post-glacial erosion of the till by ordinary atmospheric 
forces, but rather a frontal-plain deposit which accumulated rapidly 
after the ice had retreated to some .distance northward but was yet able, 
in its later dissolution, to swell all the streams. The fine material he 
considers may have been largely of super-glacial pos6 before it left the 
ice. 
Prof. Stone has given very careful and thoughtful attention to the 
coastal deposits of Maine, as correlated with the glacial epoch, and he 
has added much that will enter into the solution of questions that are 
very prominent touching the nature and origin of a series of bods lately 
named the "Columbia formation" by McGee, and their relations to the 
"Champlain" clays of Hitchcock as well as to the Laurentian and 
Algonquin of Desor. 
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