. Bulletin of the Geological Society of America. Geology. Section across Lookout-Wills'' Valley, Alabama, at the Col. The incision in the tableland of Carboniferous sandstone here is about 4 miles wide and 500 feet deep. From this section, for many miles downward in both directions, the general slope of the floor of the united valley is about ten feet per mile, so that the tableland presents bold escarp- ments more than 1,000 feet above the lower reaches of the rivers. It is an anticlinal valley. ical muds have been washed by the rains into the larger streams and, suspended in the waters, they
. Bulletin of the Geological Society of America. Geology. Section across Lookout-Wills'' Valley, Alabama, at the Col. The incision in the tableland of Carboniferous sandstone here is about 4 miles wide and 500 feet deep. From this section, for many miles downward in both directions, the general slope of the floor of the united valley is about ten feet per mile, so that the tableland presents bold escarp- ments more than 1,000 feet above the lower reaches of the rivers. It is an anticlinal valley. ical muds have been washed by the rains into the larger streams and, suspended in the waters, they have been transported out of the valleys and deposited on flood-plains or in the sea. Occasionally the streams undermine the banks and obtain extraordinary cargoes, but the principal widening agents are the rains and rills that everywhere wash away the surface and undermine the mountain sides, which action is intermittently retarded by the temporary protection of the unremoved materials of the. Little Sand Mt. VerUcaJt Feet Figure 2.—Section from Pigeon to Little Sand Mountain, Georgia. This section represents a valley of about a dozeu miles in width, with the complex geologic base shown in the figure. It illustrates well how the valleys in the southern Appalachians are produced by atmospheric denudation and not by mountain folding. landslides. While the tablelands are high, the streams are constantly deepening their channels, but when the bottoms of the ravines are re- duced to the baselevel of erosion, then the streams almost cease to corrade and become geologic carriers of the surface washings of the valley. In the recently elevated mountains of Cuba and Jamaica, as in the older Appalachian chain, the valley-making forces have overcome the physical structure, so that the valleys are more or less independent of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these
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