NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 17 



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

 of unconformity. Notwithstanding the Hthological and faunal 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 indi- 

 cation of stratigraphic discordance. The change in the Hthological 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 m which were deposited the marine 'Albany' sediments. The interrelations 

 ot the two kinds of sediments suggest oscillation of the shore-line upon a relatively 

 wide coastal plam. These changes may be explained as the result of oscillations 

 ot the land surface, or, possibly better, by the slow, but intermittent, sinking of 

 the coastal plain." 



In a later paper Gordon" 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 forma- 

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

 m hthologic character and to thickness of beds. In the Colorado Valley, inter- 

 stratified with the sandstones, clays, and conglomerates, are six or more beds of 

 limestone, each from s to 25 feet thick and all aggregating a thickness of 100 to 

 ISO 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 correspond- 

 ing 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 repre- 

 sented apparently by irregular nodular masses of earthy Kmestone in a matrix of 

 clay. With the thinning out of the limestones the shales and sandstones increase 

 in thickness. In Stephens County and farther south the shales are prevaiKngly 

 blue and the sandstones gray. Red Beds are dispersed sparingly through the for- 

 mation. 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." 



Gould,'' in discussing the relation of the limestones of Kansas and 

 eastern Oklahoma, describes the change to the red sandstones and shales 

 in several papers. 



"While the flint hills in Kansas consist almost entirely of Hmestones and shales, 

 still on the southern line of the State sandstones have already begun to appear. 

 To the south, these conditions obtain more and more until the limestone is entirely 

 replaced by sandstone. * * * South of the State line, the sandstones from the 

 east and the Red Beds of the west begin to approach each other, while the limestone 



"Gordon, U. S. Geological Survey, Water Supply and Irrigation Paper No. 317, pp. 18-20, 1913. 

 ■> Gould, Notes on the Geology of the Seminole, Creek, Cherokee, and Osage Nations, Amer. Jour. Sci., 

 vol. 11, p. 185, 1901. 



