. Bulletin. Natural history; Natuurlijke historie. PALEOGEOGRAPHY 43 4. The persistence of the lower three Thermopolis members northward. Al- though they were not studied in detail north of Wyoming, their thickness appears to be consistent northward, and they are probably continuous with part of the Mannville formation of Alberta. 5. The direction of drainage in the interior prior to the transgression. This direction was almost surely to the north (figure 10). MONTANA . I y\l rz-"-^ 1 SOUTH , \ ^ \ /^^^ BLACK / \»ORn\ I I ^, HILLS DAKOTA ; :^BASIN \ \ j ;. 3 --! I ! - I WYOMING I ' r L_.
. Bulletin. Natural history; Natuurlijke historie. PALEOGEOGRAPHY 43 4. The persistence of the lower three Thermopolis members northward. Al- though they were not studied in detail north of Wyoming, their thickness appears to be consistent northward, and they are probably continuous with part of the Mannville formation of Alberta. 5. The direction of drainage in the interior prior to the transgression. This direction was almost surely to the north (figure 10). MONTANA . I y\l rz-"-^ 1 SOUTH , \ ^ \ /^^^ BLACK / \»ORn\ I I ^, HILLS DAKOTA ; :^BASIN \ \ j ;. 3 --! I ! - I WYOMING I ' r L_. i_ FRONT^2, \ UTAH I '^^'^^^ / .' FOOTHILLS ^ I I j COLORADO I I NEBRASKA JL. Figure 10. Direction of pre-Cheyenne sandstone drainage in western Kansas prior to the initial transgression of tlie Lower Cretaceous (rusty beds) sea (based on data from Merriam, 1955). During the time the three lower members were being deposited, there must have been a drainage divide between the boreal sea in Wyoming and the Gulf Coast sea far to the south. Early Cretaceous physiography in western Kansas helps to locate this divide. In western Kansas, the Jurassic Morrison formation lies on Permian and Triassic rocks north of a line extending northeastward from the southwest corner of the state (Merriam, 1955, fig. 3). Over these Jurassic, Triassic and Permian rocks lies the Lower Cretaceous Cheyenne sandstone. The Cheyenne is in turn overlain by the Kiowa shale, followed by the Cruise sand- stone, the Huntsman shale, and succeeding units. The Cheyenne varies greatly in thickness because it fills topographic irregularities on a post-Morrison erosion. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Peabody Museum of Natural History. New Haven : The Museum
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