. Bulletin of the Geological Society of America. Geology. 88 C. E. KEYES INTERMONT PLAINS OF THE ARID REGION fuKS posed at the foots of the longer slopes, eroded from their summits. These blocks are not simple residual elevations, since they have been partly reared through recent and profound faulting. How much of such mountains should be ascribed to strictly residual effects and how much to elevation above the adjoining plains would have to be determined in each particular instance. Ordinary desert-leveling has been greatly compli- cated by extensive extravasation as well as by profound eroge
. Bulletin of the Geological Society of America. Geology. 88 C. E. KEYES INTERMONT PLAINS OF THE ARID REGION fuKS posed at the foots of the longer slopes, eroded from their summits. These blocks are not simple residual elevations, since they have been partly reared through recent and profound faulting. How much of such mountains should be ascribed to strictly residual effects and how much to elevation above the adjoining plains would have to be determined in each particular instance. Ordinary desert-leveling has been greatly compli- cated by extensive extravasation as well as by profound erogenic move- ments. The specific effects of epeirogenic movement have never been considered. The observation is made by Davis^^ that "no special conditions need be postulated as to the initiation of an arid C3^cle. The passive earth's crust may be (relatively) uplifted and offered to the sculpturing agencies with any structure, any form, any altitude, in dry as well as in moist ; While this statement is eminently true under conditions of a wet cli- mate, a little reflection must make it clear that it is not necessarily so with respect to a dry country, where the dominent erosive agency is entirely distinct. In an arid climate, accord- ing to the writer just quoted, the typical initial condition of the earth's surface is that of a more or less rugged mountainous region.^^ In a moist climate, in which there is a suc- cession of completed cycles, the most typical initial condition of surface relief is that of a peneplain. Instead of postulating similar topographic types, the beginnings of the normal and the special cycles are considered as taking place under the most antithetical of relief effects possible. This surely is not necessarily so. For the initiation of an arid cycle the selection of an antithetical type of relief instead of a normal type, as would naturally be expected, ap- pears to be due largely to deductions resting upon present conditions obtaining in
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