o34 R. T. HILL GEOLOGY OF RED RIVER. 



marls, show that the Trinity subsidence continued until the conditions 

 for deeper clear water deposits had been reached. 



The Paluxy sands show a return to the littoral conditions of the 

 Trinity and the beginning of a second subsidence. The Walnut clays 

 that succeed them show slightly deeper and further off-shore sedimenta- 

 tion. The massive chalky Goodland limestones show a still deeper and 

 quieter condition of sedimentation. These three beds (Paluxy, Walnut 

 and Goodland) represent a progressive subsidence during Fredericksburg 

 time, until the ocean was comparatively deep over central Texas and 

 its western shore was far westward toward the Rocky mountain region. 



The Kiamitia clays mark the beginning of the progressive shallowing 

 daring the Washita time. They show a shallowing condition after the 

 deposition of the Goodland limestones and a return to those prevailing 

 when the Walnut claj^s were deposited — even shallower, for there is less 

 of the fine lime precipitate and more carbonaceous matter in them. 



The Duck Creek chalks again indicate subsidence, like the Goodland 

 limestone, but to a less degree, as they are not so pure a chalk. The 

 alternations of marly clays and limestones in the overlying Fort Worth 

 limestones shows long continued shallowing. 



The Marietta beds reveal the progression of this shallowing to a more 

 littoral stage, finally culminating in the North Denison sands, when the 

 material and excessively littoral fauna indicate the nearest approach to 

 land conditions. 



The Paw Paw shales show that slight subsidence had again begun, 

 which was slightly deepened during the Main street limestone epoch, 

 after which there was a general return to land conditions which prevailed 

 throughout the region before the second grand subsidence or that of 

 Upper Cretaceous time began. 



This mid-Cretaceous epirogenic elevation could not have been of long 

 continuance, but it must have been of great magnitude and of sufficient 

 duration to completel}^ destroy the faunal continuation of the marine 

 life of the Lower Cretaceous. The interpretation of the effects of this 

 movement in the Cordilleran history of our continent is one of the most 

 important geologic problems of the future. 



The Dakota, like the Trinity, is .a deposit at marine baselevel ; estua- 

 rine, littoral and lacustral probably in places, but historically recording 

 the shallowest deposits and marking the second grand Cretaceous inva- 

 sion of the west by the Atlantic shoreline and the commencement of the 

 second or Upper Cretaceous epirogenic subsidence. 



The blue clays of the Eagle Ford shales (Benton) represent the pro- 

 gressive deepenin2:, and the Austin (Niobrara) chalk represents the cul- 

 mination of this subsidence. The overlying Ponderosa marls and beds 



