146 PROCEEDINGS OF WASHINGTON MEETING. 



the term " kames " to the knolls, hillocks, and short ridges of sand and gravel which 

 were heaped at the months of glacial brooks and rivers where they left their ice- 

 walled channels and were spread out more widely, thereby losing their velocity 

 and carrying power, on the adjoining land surface. These deposits are frequent on 

 many portions of the general drift sheet, but they are most fully developed in con- 

 nection with the terminal moraines. 



Osars or Eskers. — Prolonged ridges of gravel and sand, or in some tracts of finer 

 silt, narrow anil bordered by steep slopes on each side, called osars or eskers, owe 

 their form to deposition in the channels of glacial rivers, walled by ice, but 

 commonly open to the sky.* These peculiar ridges have a great development in 

 Sweden and Ireland, whence their names come, and in Maine, where series extend- 

 ing 100 to 150 miles have been described by Professor George H. Stone.t They are 

 well exhibited also in the valleys of the Merrimack and Connecticut rivers and 

 elsewhere in New England, but are less frequent on the nearly flat expanses of the 

 upper St. Lawrence and Mississippi basins. Associated plains of gravel and sandj 

 terminating in steep escarpments, which descend to adjacent lower land, were 

 deposited in broad embayments of the waning ice-border. 



Valley Drift. — In the valleys and on the lowlands uncovered by the departing 

 ice extensive flood-plains of gravel, sand, and clay were spread by the waters of 

 the glacial melting and the accompanying abundant rains. These deposits slope 

 with the present streams, but often somewhat more rapidly ; and they continue in 

 large valleys to the sea or to the areas of lakes that were pent up against the reced- 

 ing ice-sheet, and there form deltas and, farther offshore, sediments. Since the 

 departure of the ice, river erosion has carved the valley drift into terraces, and the 

 streams now flow far below their levels of the Champlain epoch. 



Loess. — The finest portion of the valley drift, especially where it contains some 

 glacially comminuted rock flour from calcareous formations, is called loess. In the 

 Mississippi and Missouri valleys and on the Rhine this deposit is clearly in large 

 part of glacial origin, being directly supplied from englacial drift ; but very similar 

 fluvial beds are now being formed by the Nile, and were formerly spread in great 

 thickness by the rivers of China, where the origin of the silt is referable wholly or 

 chiefly to subaerial denudation 



Deltas. — The marine delta deposits of the rivers of Maine, and the marine claya 

 which are spread extensively along the Maine seaboard to a height about 230 feet 

 above the present sea level, were chiefly derived, according to Stone, from engla- 

 cial drift. Likewise, the great deltas brought by the Assiniboine, Pembina, Shey- 

 enne, and other rivers into the glacial Lake Agassiz are largely modified drift from 

 the ice-sheet and in less amount alluvium from ordinary river erosion. South of 

 Maine much modified drift was borne into the ocean by the Merrimack, Connecti- 

 cut, Hudson, and other rivers, while their portion of the coast was more elevated 

 than now, so that their marine sediments are still beneath the sea. 



All these modified drift deposits are distributed in accordance with the laws of 

 aqueous sedimentation. The kames and eskers, having been laid down in the ice- 

 walled mouths and channels of glacial rivers, now lie as hillocks and ridges, which 



♦Proceedings Boston Society of Natural History, vol. xxv, 1891, pp. 23.S-242. 



t Proceedings Boston Society of Natural History, vol. xx, 1880, pp. 130-469, with map; Proc. Am. 

 Assoc, for Adv. of Science, vol. xxix, for lsso, pp. 510-519, with map. Am. Jour. Sei., 3d series, vol. 

 xl, 1890, pp. 122-141. 



