. Elements of geology : a text-book for colleges and for the general reader. Geology. 56 AQUEOUS AGENCIES. jammed between the glacier and the confining rocks, partly fall into crevasses and work their way to the bed, and partly are torn from the rocky bed itself. But on the other hand, on account of their slow mo- tion, glacier-erosion is by force of pressure, while that of water is by force of impact. The effects of glacier-erosion differ entirely from those of water : 1. Water, by virtue of its perfect fluidity, wears away the softer spots of rock, and leaves the harder standing in relief; w
. Elements of geology : a text-book for colleges and for the general reader. Geology. 56 AQUEOUS AGENCIES. jammed between the glacier and the confining rocks, partly fall into crevasses and work their way to the bed, and partly are torn from the rocky bed itself. But on the other hand, on account of their slow mo- tion, glacier-erosion is by force of pressure, while that of water is by force of impact. The effects of glacier-erosion differ entirely from those of water : 1. Water, by virtue of its perfect fluidity, wears away the softer spots of rock, and leaves the harder standing in relief; while a glacier, like an unyielding rubber, grinds both hard and soft to one level. This, however, is not so absolutely true of glaciers as might be supposed. Glaciers, for reasons to be discussed hereafter, conform to large and gentle inequalities of their beds, though not to small ones, acting thus like a very stiffly viscous body. Thus their beds are worn into very remarkable and characteristic smooth and rounded depressions and elevations called roclies moutonnees (Fig. 45). Sometimes large. Fig. 45.—Koches Moutonnees of an Ancient Glacier, Colorado (after Hayden). and deep hollows are swept out by a glacier at some point where the rock is softer or where the slope of the bed changes suddenly from a greater to a less angle. If the glacier should subsequently retire, water accumulates in these excavations and forms lakelets. Such lakelets are common in old glacial beds. 2. The lines produced by water-erosion, if detectible at all, are always more or less irregular and meandering; while those produced by glaciers are straight %xA parallel (Fig. 46). Thus, smooth, gently-billowy surfaces, marked with straight, parallel. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original LeConte, Joseph, 1823-1901. New York :
Size: 1739px × 1436px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
