Geology . strictsassorted drift is sufficiently prevalent and continuous at this horizonto give rise to local systems of flowing wells. Near the typical locali- 1 Geikies Ice Age, 3d ed., and Jour. Geol., Vol. Ill, p. 241. 2 Williams, E., Proc. Am. Phil. Soc, Vol. XXXVII (1898), p. 84. 3 Salisbury, Annual Report of State Geol. of N. J., 1893. 4 The Albertan drift (province of Alberta, Can.), formerly thought to be the proba-ble equivalent of the sub-Aftonian, is probably not of glacial origin. Calhoun, unpub-lished data. 6 Eleventh Ann. Report U. S. Geol. Survey. THE PLEISTOCENE OR GLACIAL PER
Geology . strictsassorted drift is sufficiently prevalent and continuous at this horizonto give rise to local systems of flowing wells. Near the typical locali- 1 Geikies Ice Age, 3d ed., and Jour. Geol., Vol. Ill, p. 241. 2 Williams, E., Proc. Am. Phil. Soc, Vol. XXXVII (1898), p. 84. 3 Salisbury, Annual Report of State Geol. of N. J., 1893. 4 The Albertan drift (province of Alberta, Can.), formerly thought to be the proba-ble equivalent of the sub-Aftonian, is probably not of glacial origin. Calhoun, unpub-lished data. 6 Eleventh Ann. Report U. S. Geol. Survey. THE PLEISTOCENE OR GLACIAL PERIOD. 385 ties named, great masses of this assorted material were plowed upby the succeeding Kansan ice-sheet and incorporated in its till, as shownin Fig. 511. The organic remains in the interglacial beds seem toimply a cool temperate climate, but as a cool temperate stage mustbe passed through twice in every transition from a glacial climateto a warm one and back again, organisms indicating a cool climate. Fig. 510.—Section of drift at Thayer, Union County, la. The stratified drift below,making up the larger part of the section, is Aftonian. It is overlain by Kansantill. (Calvin, Iowa Geol. Surv.) do not necessarily show how great an amelioration may have beenreached, unless the record is known to be complete. The length ofthe Aftonian interval has not been well determined, from lack of ade-quate accessibility, but it was at least a notable interval. The pebblesare much decayed and the soils, peat, etc., imply a considerable lapseof time. The old drift in western Pennsylvania doubtfully referred to thesub-Aftonian stage is in somewhat like manner associated with impor- 3S6 GEOLOGY. tant gravel deposits, and streams of valley gravels stretch far downthe drainage courses thai then led away from the ice-edge. This isnotably true of the Allegheny and Ohio valleys. These old glacialgravels arc so related to the present trenches of these streams as toseem to imply a channel erosio
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