. Annual report of the United States Geological Survey to the Secretary of the Interior . RETACEOUS PALEOPLAIN. 363 WICHITA PALEOPLAIS*. Wherever contacts are seen between the overlying Cretaceous rocksand the underlying Paleozoic rocks they are found to be unconform-able, and inasmuch as the same stratum of Cretaceous rocks rests indifferent places upon the planed-off edges of different layers of thePaleozoic rocks, the conclusion is reached that the Paleozoic rocksendured a long period of erosion prior to the deposition of the Cre-taceous rocks, and that this erosion took place during an int
. Annual report of the United States Geological Survey to the Secretary of the Interior . RETACEOUS PALEOPLAIN. 363 WICHITA PALEOPLAIS*. Wherever contacts are seen between the overlying Cretaceous rocksand the underlying Paleozoic rocks they are found to be unconform-able, and inasmuch as the same stratum of Cretaceous rocks rests indifferent places upon the planed-off edges of different layers of thePaleozoic rocks, the conclusion is reached that the Paleozoic rocksendured a long period of erosion prior to the deposition of the Cre-taceous rocks, and that this erosion took place during an interval oftime before the invasion of the Paleozoic rocks by the Cretaceous erosion epoch, as we know by the absence of marine Triassic andJurassic sediments, must have extended through a vast interval oftime. It is also logical to surmise that the degraded Paleozoic landwas once much higher, and that it once possessed irregularities of sur-face, which were lowered and smoothed down towaixl the general levelof the sea (base-leveled). An old eroded land surface of this character. Fig. 36.—Uncovered Wichita paleoplain, Ardraore, Indian Territory. may be geologically termed a paleoplain, and we may call this particu-lar pre-Cretaceous surface which underlies all the East-Central, Cen-tral, and Great Plains provinces the Wichita paleoplain. RESTORATION OF CONFIGURATION OF PALEOPLAIN. Too little is as yet accurately known of the Wichita paleoplain tooutline correctly its concealed configuration, but sufficient is knownto state that it represents what was once an extensive land area inJurassic time which was base-leveled and invaded by the sea in Cre-taceous time. That portion making the Paleozoic floor of the Blackand Grand prairies is only a part of the entire vast paleoplain whichoccupies all of what is the present Greater Plains region lying betweenthe old nuclei of the Cordilleras on the west and an indefinite boundarysituated somewhere east of the present Black Prairie
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