. A second visit to the United States of North America . ca schist in beds with subordinate layers, both horizontal andoblique, was originally determined, in most cases at least, byaqueous deposition, although often modified by subsequent crys-talline action. The surprising depth of some of the modern ravines, in theneighborhood of Milledgeville, suggests matter of curious specula-tion. At the distance of three miles and a half due west of thetown, on the direct road to Macon, on the farm of Pomona, isthe ravine represented in the amiexed wood-cut (p. 29). Twentyyears ago it had no existence ;
. A second visit to the United States of North America . ca schist in beds with subordinate layers, both horizontal andoblique, was originally determined, in most cases at least, byaqueous deposition, although often modified by subsequent crys-talline action. The surprising depth of some of the modern ravines, in theneighborhood of Milledgeville, suggests matter of curious specula-tion. At the distance of three miles and a half due west of thetown, on the direct road to Macon, on the farm of Pomona, isthe ravine represented in the amiexed wood-cut (p. 29). Twentyyears ago it had no existence ; but when the trees of the forestwere cut down, cracks three feet deep were caused by the sunsheat in the clay ; and, during the rains, a sudden rush of waterthrough these cracks, caused them to deepen at their lower ex-tremities, from whence the excavating power worked backward,till, in the course of twenty years, a chasm, measuring no lessthan 55 feet in depth, 300 yards in length, and varying in width Chap. XXL] RAVINE NEAR MILLEDGEVILLE. 29 Fig. Ravine on the Farm of Pomona, near Milledgeville, Georgia. January, in the last twenty years, 55 feet deep, and 180 feet broad. 30 MODERN RAVINES. [Chap. XXL from 20 to 180 feet was the result. (See fig. 7, p. 29.) Thehigh road has been several times turned to avoid this cavity, theenlargement of which is still proceeding, and the old line of roadmay be seen to have held its course directly over what is nowthe widest part of the ravine. In the perpendicular walls of thisgreat chasm appear beds of clay and sand, red, white, yellow,and green, produced by the decomposition in situ of hornblendicgneiss, with layers and veins of quartz, as before-mentioned, andof a rock consisting of quartz and felspar, which remain entire toprove that the whole mass was once crystalline. In another place I saw a bridge thrown over a recently formedgulley, and here, as in Alabama, the new system of valleys andof drainage, attendant on
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