NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 89 



are foimd on or in the sand layers were evidently washed there by currents from a 

 distant shore, and they are generally more or less imperfect, having been dispersed 

 by the action of the current or by predatory animals, while those found in clay 

 were evidently animals which mired down on wide mud flats or were drifted out 

 on the surface of the stagnant lagoons.' 



The clays and the sandstones are separated in some places by unconformities 

 which are considered by Case to be the result of currents that eroded channels in 

 the clay in which the sands were afterward deposited. They do not represent appar- 

 ently any considerable time interval between the two deposits. Moreover, the 

 conglomerates containing concretions of ferruginous clay are evidently additional 

 indications of transitory currents in an ordinarily quiet lagoon or over the tidal flats 

 of a wide delta. 



The red sediments evidently had their source in the degradation of the Wichita 

 Mountains, which lie directly to the north of this region, in Oldahoma. These 

 mountains were uplifted during or at the close of the Pennsylvanian epoch and are 

 now, together with their accompanying elevations on the east, the Arbuckle Morm- 

 tains, partly buried in the sediments they have furnished. 



The fact that in this region, as shown by their outcrop toward the east and by 

 the strata penetrated in deep wells, the upper beds of the Cisco formation consist 

 of sediments corresponding in character to those of the Wichita formation, suggests 

 that mud fiats may have characterized the closing stages of the Pennsylvanian epoch 

 in this region. 



"Thickness. — In Shackelford County the thickness of the Wichita formation is 

 estimated to be i,ooo to 1,200 feet. Two-thirds or more of the formation consists 

 of blue clays and shales. Farther south, in the vicinity of Colorado River, lime- 

 stones constitute the major part of the formation. To the north from Shackelford 

 County the calcareous sediments diminish, and before reaching the Oklahoma 

 border they practically disappear. No reliable estimate can be made of the thick- 

 ness of the formation in this part of the region, though it is probably not less than 

 1,500 feet." 



South of the north line of Oklahoma the Permo- Carboniferous beds dis- 

 appear beneath the Triassic at the eastern side of the Staked Plains (plate 13, 

 fig. i). On the western side of the Staked Plains Permo-Carboniferous beds 

 appear in the valley of the Pecos River, according to Beede (see p. 58), but 

 they are absent in the latitude of Tucumcari, Montoya, and Las Vegas. Ap- 

 parently the condition of river and delta deposits extended across the Staked 

 Plains and west to the Rocky Mountains south of this latitude as it did to 

 the north, but here there is no certainty that it reached to the mountains. 



As outlined above (pp. 62-71), the Red Beds of Permo-Carboniferous age 

 in the northern part of the Plains Province shade into limestones toward the 

 east and north, indicating the western edge of the open-sea waters. There 

 seems little doubt that the northern Red Beds are connected with those in 

 the south beneath the later deposits, and that both are parts of one great 

 area of deposition. 



Beyond the Rocky Mountains red bed conditions prevailed along the 

 Chama River in Rio Arriba County, New Mexico, and probably much farther 

 to the north and south, though this may have been in a slightly earlier time. 



