370 GEOLOGY OF NORTHWESTERN TEXAS. 



The formation includes all kinds of sedimentary rocks, with shales, clays, 

 and seams of coal. There is no regular order in which these various beds 

 occur. In the northern part of the formation in the State there are no lime- 

 stones. In the southern part of the northern field there are first limestones, 

 then sandstones, then beds of limestones, and at the base heavy beds of blue 

 clay and limestones. 



In the central district there are first limestones, and then heavy beds of 

 clay and sandstones, and at the base beds of blue limestones. 



There is no evidence whatever that the border formations on the south- 

 ward of the present Carboniferous were ever overlaid by the Cretaceous 

 Measures. All the evidence is directly to the contrary. It is evident that 

 the present Silurian fields constituted the dry land during the whole of the 

 Carboniferous Era. There was, in all proability, at the southern part of the 

 Coal Fields in Texas an island in the Carboniferous sea, the extent of which 

 it is now impossible to determine, for the reason that all the country south of 

 the older rocks are covered by those of a later period than the Carboniferous. 



There is no reason to suppose that the eastern shore line of the Carbonif- 

 erous sea was anywhere in the region of the present eastern border of the 

 Carboniferous formation in Texas. The great interior of the continent, from 

 the Appalachian region to the western borders of Kansas and Nebraska, was 

 slowly emerging from the waters during the era of the Coal Measures. At 

 that time the Coal Fields were probably one vast forest, with here and there 

 lakes of fresh water, and the deep water was farther to the southward than 

 has ever been discovered. 



Although the era was one of comparative quiet, with very slow emergence 

 and submergence of the continental area, yet at the close of the Carboniferous 

 period there had been formed a shore line extending from the northeastern 

 part of the continent to the older formations in Llano County, cutting off a 

 large area in which there was an interior sea in which the strata of the Per- 

 mian and Triassic were afterward deposited. That barrier was probably 

 formed not only by the deposition of material from the waters, as was the 

 case over the entire region, but was probably assisted by a fold making an 

 anticlinal and giving a northwestward dip to the Carboniferous strata that it 

 has retained until now. 



It is probable that the Cretaceous sea, that came on at a later date, did not 

 cover up the entire area of the Carboniferous and Permian, but was rather in 

 deep seas off the shores of these land areas. The erosion of the Cretaceous 

 over large areas since that time has obscured the evidences of the extent of 

 the Cretaceous seas, but I am inclined to think the Cretaceous seas extended 

 in a narrow belt across the southern border of the Carboniferous, but doubt 

 if the sea extended as far north as the Wichita River. 



