Bulletin of the Geological Society of America . and in The Potholes. The current whichemerged from the Potholes themselves spread considerably over this ter-race and spilled over its edge in a broad sheet which later became some-what concentrated in four or five different places, so that minor notchingof the edge of the terrace resulted; but none of these notches was cutback more than a quarter of a mile. Above and east of the upper falls is a scabland tract extending twomiles farther east across the low rim of the structural basin and verymuch diversified by ramifying channels and their separ
Bulletin of the Geological Society of America . and in The Potholes. The current whichemerged from the Potholes themselves spread considerably over this ter-race and spilled over its edge in a broad sheet which later became some-what concentrated in four or five different places, so that minor notchingof the edge of the terrace resulted; but none of these notches was cutback more than a quarter of a mile. Above and east of the upper falls is a scabland tract extending twomiles farther east across the low rim of the structural basin and verymuch diversified by ramifying channels and their separating are common, some of them being 40 feet deep. This chan-. FiGURE 10.—One of The Potholes The gravel bar (terrace on left) is 200 feet thick and the clifE back of it is 200 feethigh. View is taken looking toward the ancient cataract. neled tract was an island-studded rapids descending to the brink of ThePotholes cataract. At the beginning of the cataract this channeledarea extended to the original edge of the upper terrace. As the twinfalls, narrower than the channel group, receded eastward, some of thesechannels were left along the edge of tlie gorge. The talus accumulations of The Potholes are somewhat irregularin height, because of unusually marked differences among the flows inthe cliffs, but the large majority constitute three-fourths or more of thetotal height of the cliffs (see figure 7). The Potholes cataract wasformed at the time of the Spokane glaciation by discharge from theQuincy basin. The Columbia Valley here was nearly or quite as deepat that time as it is today. The structural basin was aggraded to thelevel of this western r
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
