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Report of the Secretary of Agriculture in relation to the forests, rivers, and mountains of the southern Appalachian region

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  • 120 SOUTHERN APPALACHIAN REGION. the Archean, or oldest known age. The different rocks include several kinds of granite, diorite, mica-gneiss, hornblende-gneiss, and various schists. A large number of these are of igneous origin, but the original nature of many of the gneisses and schists is unknown. Formations also included in this group are the ancient volcanic rocks. These are developed most prominently in connection with the Cambrian quartzites in the northeastern part of the mountain district. RELATION OF ROCKS TO SURFACE. rocks1.""0" 0t Much of the surface of the Appalachian Mountains is exceedingly ancient. During the later geologic periods it has been subjected to the various natural agencies of destruction and has been worn down according as the rocks presented at the surface were susceptible to these influences. The materials composing these formations are attacked in varying degrees by solution and by chemical processes connected with atmospheric and underground water. Certain minerals—for instance, carbonate of lime—are readily dissolved by natural waters, and the rock in wasting away leaves behind only the less soluble portions in forms of clay. To this capability is directly due the reduction of the Great Valley below the mountain mass. Other minerals—for instance, feldspar—are in part dissolved and in part chemically altered and decomposed by natural waters, so that the coherence of the rock which contains them is largely destroyed. Two groups in this region have a large proportion of feldspar in their makeup, and their surfaces have been gradually lowered by its breaking down. These are the Ocoee group and the Archean group. A third mineral—quartz—is comparatively little changed by solution or chemical action near the surface. Formations made up in large part of this mineral retain their altitudes most persistently and are usually the last to be reduced. This composition is most pronounced in the Lower Cambrian group, but is shared also by the Ocoee group and the Archean group. Although the thickness of the Lower Cambrian quartzites is so much less than that of the other groups, their resistance to solution has caused them to remain upheld in very high ridges and peaks. To this are due the cliffs of Chilhowee, Camp Creek, and Iron mountains and the rugged crags of Grandfather. In the case of the Ocoee and Archean groups their immense thickness and the amount of quartz which
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Object’s are ‘parent’ level descriptions to ‘children’ items, (e.g. a book with pages).