Geology . Fig. 485.—Tortuous glacial grooving. The gorge is believed to be due to a sub-glacial stream, into the channel of which the ice settled down, moulding itselfto the gorge and grooving it. Kelleys Island, Lake Erie. (U. S. Geol. Surv.) (Fig. 484). The direction of striae corresponds with the direction inwhich the drift was transported. Sometimes stria) and grooves follow narrow and tortuous gorges(Fig. 485). Striae are not confined to horizontal or even to gentlyinclined surfaces. They occur on steep slopes (Fig. 486), not infre-quently on the vertical faces of cliffs, and, occasionall
Geology . Fig. 485.—Tortuous glacial grooving. The gorge is believed to be due to a sub-glacial stream, into the channel of which the ice settled down, moulding itselfto the gorge and grooving it. Kelleys Island, Lake Erie. (U. S. Geol. Surv.) (Fig. 484). The direction of striae corresponds with the direction inwhich the drift was transported. Sometimes stria) and grooves follow narrow and tortuous gorges(Fig. 485). Striae are not confined to horizontal or even to gentlyinclined surfaces. They occur on steep slopes (Fig. 486), not infre-quently on the vertical faces of cliffs, and, occasionally, even on theunder sides of overhanging rock masses. 350 GEOLOGY. Besides the Btria>, grooves, etc., on the bed rock, there are oftenother details of surface which are equally characteristic. Minute. Fig. 486.—Striae on two contiguous surfaces which meet each other at a large shore of Kelleys Island, Lake Erie. (U. S. Geol. Surv.) protuberances of surface often show more wear on one side than onthe other (Fig. 487 and 488). Minute depressions (Fig. 488), show
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