THE PLAINS PROVINCE 97 



County they outcrop in the bank of the river about a mile from the post-office. 

 Here the beds show a local gradation into sandstone, suggesting near-shore condi- 

 tions of sedimentation. * * * 



"Nowhere in the southern area, so far as observed, are there any indications 

 of unconformity. Notwithstanding the lithological and fauna! characteristics 

 which distinguish the 'Albany,' these beds appear perfectly conformable with 

 the Cisco below and the Clear Fork above, nor is there within the formation any 

 indication of stratigraphic discordance. The change in the lithological character 

 of the beds toward the north is evidently the result of differences in the conditions 

 of sedimentation. The character of this part of the formation suggests very 

 strongly its origin on a coastal plain, or river delta, to the south and west of which 

 lay the sea, in which were deposited the marine 'Albany' sediments. The inter- 

 relations of the two kinds of sediments suggest oscillation of the shore-line upon 

 a relatively wide coastal plain. These changes may be explained as the result 

 of oscillations of the land surface, or, possibly better, by the slow, but inter- 

 mittent, sinking of the coastal region." 



In a later paper Gordon 1 further discussed this point: 



"A feature of importance in the Cisco formation, and one which it shares 

 with the next succeeding formation, is the series of changes observed as the 

 formation is traced northward along the strike. These changes relate both to 

 variation in lithologic character and to thickness of beds. In the Colorado 

 Valley, interstratified with the sandstones, clays, and conglomerates, are six or 

 more beds of limestone, each from 5 to 25 feet thick and all aggregating a thick- 

 ness of 100 to 150 feet. In the southern part of the Brazos Valley the calcareous 

 divisions are only about half as thick as they are farther south, and the clays show 

 a corresponding increase in thickness. In Young County the calcareous material 

 diminishes northward at an increased rate until, at the northern boundary of the 

 county, the limestones have practically disappeared, and beyond that point they 

 are represented apparently by irregular nodular masses of earthy limestone in a 

 matrix of clay. With the thinning out of the limestones the shales and sand- 

 stones increase in thickness. In Stephens County, and farther south, the shales 

 are prevailingly blue and sandstones gray. Red Beds are dispersed sparingly 

 through the formation. The blues gradually give place to reds until in the 

 vicinity of Red River the red color dominates. In this part of the region the 

 rocks consist, for the most part, of red sandstones, clays, and sandy shales, with 

 a few beds of blue shale and bluish to grayish-white sandstones. Limestones 

 are conspicuously absent. * * * 



"Beds of red clay make their appearance south of Young County, but they 

 increase notably to the north, especially in the upper part of the formation, along 

 with the diminution of the limestones, and they constitute the dominant feature 

 of the formation in eastern Clay and western Montague Counties." 



On the western side of the Red Beds areas of Kansas, Oklahoma, and 

 Texas the sandstones and shales pass unchanged beneath the Mesozoic and 

 Tertiary deposits of the Staked Plains. The western border of the Plains 

 Province of deposition lies close to Front Ranges of the Rocky Mountains. 



The stratigraphy of the western border of the Red Beds in the States 



1 Gordon, C. H., U. S. Geological Survey, Water Supply and Irrigation Paper No. 317, 



pp. 18-20, 1913. 

 8 



