THE SPOKANE GLACIATIOX 589 



of Crab Creek, Coal Creek, Duck Creek, Lake Creek, an unnamed creek 

 west of Lake Creek, Connawai Creek, Wilson Creek, Spring Coulee, and 

 Grand Coulee. The first eight originated from the ice on the northern 

 rim of the plateau between Hellgate and Medical Lake. The other two 

 entered the plateau from the Columbia Valley by one route, upper Grand 

 Coulee, and separated at Coulee City. The location of the edge of the 

 Spokane ice near the head of Grand Coulee is as yet unknown. 



The glacial river courses are all youthful canyons in basalt. They are 

 quite unlike the associated drainage lines of comparable length which 

 never received glacial waters and which are typical valleys in maturity. 

 The youthful canyons, however, were not eroded by the streams which 

 occupy them. Despite their size, most of them are but the deepened 

 channels of ice-born rivers, and not true valleys. Like the scablands of 

 the Palouse region, invading, but short-lived, floods traversed the area; 

 but they failed in the main to produce broad, stream-scoured surfaces of 

 bare rock. Where they entered preglacial valleys in basalt they were not 

 able to broaden them much, Extensive scablands have been formed only 

 where the preglacial drainage pattern was eroded in a weak, super-basalt 

 sedimentary deposit. 



The limits reached by the Spokane ice-sheet west of Cheney and Med- 

 ical Lake are not well known, since there is no morainal ridging along 

 the margin. The approximate boundary, as shown on the accompanying- 

 map, has been located along the southern limits of a basalt plain with 

 much bare rock and a scattering of glacial debris. South of this margin 

 are unglaciated loess-covered hills of mature aspect and the scoured, and 

 in many places canyon-like, glacial drainage channels. The limits as 

 drawn are, perhaps, too far south in places. The ice is not known to 

 have crossed the Columbia between Hellgate and the head of Grand 

 Coulee. It did cross, however, in Douglas County, farther west, and ad- 

 vanced far enough to discharge its waters into Moses Coulee. The Wis- 



bills. The tiU is covered with several feet of loess at Cheney. The loess is deep on all 

 Palouse Hills of eastern Washington, but does not occur on the scablands or on the 

 glaciated plain to the north. It therefore is older than the Spokane glaciation. Since 

 this Cheney till is beneath the loess and probably underlies the Palouse Hills, it is 

 much older than the mature topography. There is no more suggestion of glacial over- 

 riding in the shapes of these hills north of Cheney than there is in the typical Palouse 

 region of Whitman County. 



On the other hand, certain large pre-basalt hills west of Medical Lake, rising high 

 above the Palouse Hills of the region, do show a prevailingly steep northern slope and 

 gentle southern slope, as though they had been overriden by glacial ice. If this profile 

 has had such an origin, it must be ascribed to the pre-Spokane. pre-loess glaciation. 



The glacial till reported by I'ardee (op. cit.) at "scores" of places over large parts of 

 Lincoln, Spokane, and Adams counties, and as far south as Kahlotus. probably is simi- 

 larly related to the loess which deeply mantles the Palouse Hills of those counties. 



