Geology . inst their bases is often firmly cemented into brecciaby lime carbonate. The geographic conditions in the basin regionare such as to cause most of the coarser products of erosion from themountain to be deposited on the lowlands about them. If the Quater-nary talus and alluvial deposits were sharply separable from thoseof late Tertiary age, they would afford a rough measure of the Quater-nary erosion in the mountains. As the glacial deposits increase in importance to the north, talusand other subaerial accumulations become less conspicuous, and areof much less importance in Montana, I
Geology . inst their bases is often firmly cemented into brecciaby lime carbonate. The geographic conditions in the basin regionare such as to cause most of the coarser products of erosion from themountain to be deposited on the lowlands about them. If the Quater-nary talus and alluvial deposits were sharply separable from thoseof late Tertiary age, they would afford a rough measure of the Quater-nary erosion in the mountains. As the glacial deposits increase in importance to the north, talusand other subaerial accumulations become less conspicuous, and areof much less importance in Montana, Idaho, and Washington, thanin the more arid regions farther south. Talus accumulations take on various forms, as shown in Figs. 554to 556. Fig. 554 shows talus in its normal form. Fig. 555 shows atype of accumulation not uncommon in the western mountains. Insome cases at least this disposition of the talus appears to be due to 1 King, op. cit., p. 472. 2 King, op. cit; THE PLEISTOCENE OR GLACIAL PERIOD. 473. Fig. 554.—Xormal steep talus slope. sc
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