DIVISIONS OF THE STRATA. 187 



even if it can be found at all. This is no less the case with the line between 

 the Permian and the underlying Coal Measures. A separation of these series 

 from the Coal Measures is, however, based, first, on lithological differences; 

 second, on fossil contents. 



The strata of the Coal Measures are not persistent in character on the line 

 of contact between that formation and the overlying Permian; and yet in 

 each locality there seems to have been a continuous sedimentation. On the 

 line of contact between the Coal Measures and the Wichita Beds, from Red 

 River south to the Brazos, there are only sandstones in both strata; yet there 

 was a considerable lapse of time between their deposition, as is shown by the 

 fact that the limestones, which at other places constitute the highest beds of 

 the Coal Measures, and which at those places overlie the sandstones, are en- 

 tirely wanting along the line of this contact. Further south, on the line of 

 contact between the Coal Measures and the Clear Fork Beds there are only 

 limestones, which are apparently continuous in sedimentation, yet we know 

 that such is not the case, for only a few miles north of this line of observa- 

 tion we find that the Wichita Beds of the Permian underlie these Permian 

 limestones. 



The fact of the want of continuity of sedimentation between the Coal 

 Measures and the Clear Fork Beds is shown also by the fauna of the two 

 beds. The fauna of the Coal Measures limestones, which lie directly below 

 the limestones of the Clear Fork Beds, is abundant, and consists of such char- 

 acteristic forms as Productus semi-reticulatus, Chaetetes gracilis, Schizodus ivheeleri, 

 Allorisma suh-cuneata, Hemipronites crassus, etc., but they almost fade out before 

 they reach the top of the series, and only a few species pass up into the over- 

 lying limestones of the Permian, and other species of newer type take their 

 places. The same may be said of the fauna on the line of contact between 

 the Coal Measures and the Wichita Beds. 



The Double Mountain Beds do not reach the Coal Measures at any point, 

 but lie conformably upon the Clear Fork Beds. The Clear Fork Beds are 

 the only ones that reach the southern extremity of the Permian district. 



The Permian Beds are overlaid on the west by the Jura-Trias (?) and Cre- 

 taceous. It is evident from the remaining buttes and ranges of Cretaceous 

 hills that the entire Permian and Carboniferous strata were at one time cov- 

 ered by the Cretaceous, at least along the southern portion of the district. 

 Erosion has again removed these strata and exposed the older beds. 



THE WICHITA BEDS. 



The Wichita Beds are the lowest in the series, and are composed of sand- 

 stones, sandy shales, clays, and a peculiar conglomerate. The sandstones and 

 sandy shales are red, gray, and variegated, often containing large oval con- 



