REPORT OF THE STATE GEOLOGIST. lxxi 



MESOZOIC GROUP. 



JURA-TRIAS. 



The only rocks which now seem referable to the Jura-Trias, which 

 covers the period between the Permian and Cretaceous, are a fine- 

 grained red (terra-cotta) sandstone, which underlies the Trinity sands 

 in the Double Mountain, Stonewall County, and the conglomerate 

 and sandstone which have been called the Dockum Beds, from their 

 characteristic exposure at that point. This conglomerate is the water- 

 bearing bed of the Staked Plains. From it flow the great springs that 

 feed the Red, Brazos, and Colorado rivers, and from which they take 

 their rise, and their corrosive force is the power that is gradually eating 

 into the scarp of the plains and moving them backward year by year. 

 The greatest value of this bed is its water bearing quality, and it was 

 thought that enough fossils were collected from it to enable us to cor- 

 rectly determine its age and exact relations to the other strata. For 

 the present it is placed with the Terra-Cotta sandstone above as Jura- 

 Trias, as it underlies the Trinity sands. 



The deposition of these beds was followed by the opening of the 

 Cretaceous System, as shown in the Trinity sands, the accompanying 

 conditions of which may possibly have been the initial depression 

 forming the Mississippi embay men t, the extent of which was greatly 

 diminished in Mid-Cretaceous times by the elevation which brought the 

 greater part of the Lower Cretaceous to the light of day. From this 

 point we have already traced the history of our State with the excep- 

 tion of the deposit which forms the upper portion of the Staked Plains. 



This deposit, called here the Blanco Canyon beds, is composed of 

 white clays, infusorial earth, etc., containing fossil remains of verte- 

 brates (turtles and large animals). In age it probably corresponds to 

 to the upper part of the Fayette Beds, which it resembles closely in 

 some lithologic features. 



The geology of Trans-Pecos Texas cannot be discussed at this time 

 for lack of detailed knowledge. 



ARTESIAN WATER. 



From what has been written it can easily be gathered that our salient 

 geologic features may be comprised in — 

 A Ghilf Slope. 

 A Central Basin. 

 A Western Mountain System. 



