KAMES, ESKEES, AND VALLEY DRIFT. 179 



siderably above that of the main body of the ghacial lake with which 

 it became united b}' the recession of the ice-sheet. Fartlier toward the 

 northwest the g'lacial boi'der, during the Mesabi stage, and probably 

 during several later stages of pause or readvance interrupting its general 

 retreat, rested on the highlands of the Riding and Duck mountains and the 

 Porcupine and Pasquia hills, and held on its west side the glacial Lake 

 Saskatchewan, which outtlo\\'ed tlu'ough the Qu'Appelle and Assiniboine 

 rivei'S to Lake Agassi z. 



. MODIFIED OK ASSORTED DRIFT. 



The modified drift comprises sediments of gravel, sand, clay, and silt 

 that were derived directly from the ice-sheet, but were modified by cur- 

 rents of water, which assorted, transported, and deposited them. This class 

 of drift occurs in many diverse forms. Some of its beds were subglacial 

 and others were accumulated at the margin of the ice; but the writer 

 believes that far the greater part of the modified drift was englacial at the 

 time of the final melting, and was then washed away from the ice border 

 by the streams of its ablation and by rains. 



McGee^ and Chamberlin^ have judiciously proposed the restriction of 

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

 which were heaped at the mouths of 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 sm-face. These 

 deposits are frequent on many portions of the general diift-sheet, but are 

 most fully developed in connection with the terminal moraines. 



Prolonged ridges of gravel and sand, or, in some tracts, of fine silt (as 

 described by McGee in northeastern Iowa), narrow and bordered by steep 

 slopes on each side, called eskers or osars, owe their form to deposition in 

 the channels of glacial rivers walled by ice, but, the author thinks, com- 

 monly open above to the sky.' These peculiar ridges have a great develop- 

 ment in Ireland and Sweden, whence then- names come, and in Maine, 



'Report of the luteruational Geological Congress, second session, Boulogne, 1881, p. 621. 

 «U. S. Geol. Survey, Third Annual Report, for 1881-82, p. 299. Am. Jour. Sci. (3), Vol. XXVII, 

 p. 389, May, 1884. 



^Proceedings, Boston Society of Natural History, Vol. XXV, 1891, pp. 238-242. 



