Upham.] 
240 
[Feb. 18, 
surface of lakes bordering the receding ice, of which lacustrine 
class an osar extending seven miles from north to south in a 
valley of the southern Adirondacks at Chestertown, N. Y., is 
cited as an example. 1 But the fact that the osars and kames of 
southeastern Massachusetts near the coast are destitute of marks 
of shore erosion, which, according to Professor Shaler, they must 
exhibit “if they were exposed even for a few days to the action 
of the Atlantic surf and tides , ” seems, without speaking of the 
lack of marine fossils of Champlain age, to be sufficient disproof 
of his supposition that this district was covered by the sea when 
the ice disappeared. Northward from Boston, along the coast of 
northeastern Massachusetts, New Hampshire and Maine, marine 
submergence at that time is shown by fossiliferous beds overlying 
the till to a maximum height of about 230 feet in Maine ; and to 
this limit, but no higher, the osars and kames have been washed 
and remodelled by sea waves and currents. 
With the foregoing interpretation of the conditions under 
which these ridges and knolls of gravel and sand were formed, 
Prof. W. M. Davis agrees so far as to attribute them to subgla 
cial rivers ; but he finds no reason for asserting that they were 
submarine or sublacustrine. Writing of the structure and origin 
of sand and gravel plains, 2 like those enclosing Walden, Cochit- 
uate, and this class of lakes, Professor Davis describes a back- 
wardly dipping stratification of the beds forming the edge of the 
plains where they adjoined the ice-sheet, and attributes it to the 
upflow of subglacial waters bringing with them the sediments 
which make the plain and reach to a considerable distance, hav- 
ing in their lower portion on far the greater part of their area the 
forwardly dipping stratification that is characteristic of deltas or 
of deposits swept by torrential currents into the slowly flowing 
broad expanses of flooded rivers. It seems to me, however, 
more probable that the back-set beds were formed by the down- 
ward and backward transfer of sand from the surface of the plain, 
to fill in succession the small spaces from which the ice-sheet was 
gradually withdrawn. 3 
1 Proceedings of this Society, vol. xxiii, 1884, pp. 36-44. Am. Jour. Sci., III., vol. 
xxxiii, pp. 210-221, March, 1887. U. S. Geol. Survey, Seventh annual report, for 
1885-86, pp. 314-322; Ninth an. rep., pp. 549-50; Bulletin No. 53, 1889, pp. 18-21, 26, 
42-47. 
2 Bulletin, Geological Society of America, vol. i, for 1889, pp. 195-202. 
3 Compare Geology of N. H., vol. iii, pp. 131-137. 
