366 LIFE OF THE PLEISTOCENE 



declared moraines, drumlins, and other distinctive glacial formations of the 

 period. The ice radiated not only from the Labradorean, Keevvatin, and Cor- 

 dilleran centers, but from many isolated heights. Nearly all the well-known 

 mountain glaciation of the west is referred to this epoch. The drift-sheet of 

 this stage is characterized by ernormous terminal moraines, by great bowlder 

 belts, by unusual developments of kames, eskers, drumlins, outwash aprons, 

 valley trains, and other diagnostic features of glacial action and glacio-rluvial 

 cooperation. This drift-sheet, far beyond all the others, bears the stamp of the 

 great agency of the period. The disposal of the ice in great lobes is referable 

 to the influence of the great basins. Field studies indicate that broad, smooth- 

 bottomed basins, elongate in the general direction of the ice movement, favored 

 the prolongation of the ice into broad lobes, while sharp, deep valleys of tor- 

 tuous course or transverse attitude had little effect upon the extension of the 

 ice. 



"The Later Wisconsin drift is characterized in some places 2 by nearly a score 

 of concentric moraines which, in some cases, represent re-advances of the ice 

 in the course of its general retreat, and in others perhaps nothing more than 

 halts sufficient to permit an exceptional accumulation of drift at the ice border. 

 There appears to have been exceptional vigor of ice action, correlated with 

 rapidity of melting, resulting in a sharp contest between the antagonistic agen- 

 cies that made for advance and retreat. The older drift-sheets, so far as over- 

 ridden by the ice of this epoch, were cut away more largely than in preceding 

 epochs, and the scoring of the rocks below was more prevalent and profound. 

 This was notably so in the great thoroughfares of movement, and for obvious 

 reasons less so where the lateral borders of the lobes only lapped upon the older 

 drift. Extensive overriding of the older drift, without complete removal, 

 occurred in some districts, notably in Illinois and Michigan, as determined by 

 Leverett. " 



In Ohio there was a period of erosion between the two tills; the cutting of 

 the broad valley of Mad River, two miles in width and 25-50 feet in depth, is 

 referred by Chamberlin to this interval. Other river erosions in this and other 

 parts of the state are also placed in this interval. 3 



LIFE 



"As yet no soil, or leached or weathered zones have been found separating 

 the drift of the two series and it seems questionable whether the interval be- 

 tween their deposition was sufficiently long to justify their reference to distinct 

 glacial stages." 4 No life has yet been reported from this interval. However, 



2 Minnesota, Upham, 9th An. Rep. Geol. and Nat. Hist. Surv. of Minn., p. 880; Leverett, 

 Mon. XLI, U. S. Geol. Surv. 



3 Leverett, Monograph XLI, p. 352. 

 'Leverett, Illinois Glacial Lobe, pp. 317-318. 



