Bulletin of the Geological Society of America . Acad. Sciences, vol. S, 1918. pp. 411-412), argues that the falls havereceded for 17 miles, virtually the full length of the lower coulee. (504 J. H. BRETZ GLACIAL DRAIXAGE OX COLL^MBIA PLATEAU aggTaded floor. The northwest sides of these hills are notably smoothedand rounded and some bear striae. The orientation varies, as would beexpected on rugged rock hills overridden by ice, but is not far fromnorthwest-southeast. The southeast sides are steep and jagged. Thesheeted structure of the granite apparently has lent itself to plucking l)ythe ice.
Bulletin of the Geological Society of America . Acad. Sciences, vol. S, 1918. pp. 411-412), argues that the falls havereceded for 17 miles, virtually the full length of the lower coulee. (504 J. H. BRETZ GLACIAL DRAIXAGE OX COLL^MBIA PLATEAU aggTaded floor. The northwest sides of these hills are notably smoothedand rounded and some bear striae. The orientation varies, as would beexpected on rugged rock hills overridden by ice, but is not far fromnorthwest-southeast. The southeast sides are steep and jagged. Thesheeted structure of the granite apparently has lent itself to plucking l)ythe ice. Furthermore, the summits of the basalt bluffs on the westernside of the coulee also are striated in approximately the same directions,and stria? and abundant large granite erratics are reported on the top ofSteamboat Rock (figure 12). The giaciation of these granite hills and the basalt hill south of themoccurred at the maximum deployment of the AVisconsin ice on the pla-teau. It can not be a record of the Spokane giaciation, for these granite. FiGiKE 12.—^Steatuboat Rock Steamboat Rock is in the middle of the Grand Coulee and near the head. The talus is of Dost-Wiscottsin age. hills tht^n were buried hundreds of feet l)eneath basalt and have beenexhumed by the erosion of both Spokane and Wisconsin glacial it l)e argued that this exhumation occurred during the early stages ofthe Spokane giaciation, the ice later advancing into the head of GrandCoulee, the answer is that these exposed glaciated surfaces would havel)een obliterated during the interglacial interval. What became of the Wisconsin drainage when the Okanogan lol^ecrowded down into the head of Grand Coulee? Since the Spokane spill-ways to Pa louse River are lower than all others on the plateau exceptGrand Coulee, and since there was an eastward route open to them infront of the Wisconsin ice, it might be expected that for a short timeglacial drainage would be diverted to the Palouse. But reexaminationof t
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
