The Trlvitij Division. 13 



report upon the "Occurrence of Artesian Water," and much of 

 the detail of the section given in the Third Annual Report of the 

 Texas Geological Survey.* The thickness of the rocks of the 

 Trinity Division in this region is about 500 feet. The beds have 

 not been systematically studied in their extent south of the Colo- 

 rado river. 



From study of these sections it is concluded tliat the beds, as 

 a whole, indicate a progressive and continuous series of sedi- 

 ments, representing subsidence from land through littoral to off- 

 shore conditions, followed Ijy renewed shallowing at its close. 

 It consists of sands and conglomerates at its base, and grades 

 upward into magnesian and chalky limestones. No sharp lines 

 of demarcation can be drawn l)ctween the sands and limestones, 

 so imperceptibly do they merge into each other. 



The Basement Beds or Trliilln Sands proper. — These consist 

 mostly of unconsolidated line conglomerate and sands of the 

 nature locally known as pack sands, and contain, besides logs 

 of silicified wood, occasional masses of firm, lustrous lignite of 

 dei)ressed oval cross-section, like those found in the Potomac 

 Ibrmation near Muirkirk, Maryland. Large bones of vertel)rates 

 have also occasionally Ijcen found, notaljly near Millsap, Texas, 

 Travis Peak post-office, and at Gypsum Bluffs, Arkansas, which 

 arc supposed to be the remains of Dinosaurs. It was owing to 

 the occurrence of these bones that in an early jiaper these sands 

 were at first termed the Dinosaur sands b}^ the writer.f 



TJie Glen Rose Beds. — Indurated layers of impure calcareous 

 and yellow material succeed the sands, and become more calca- 

 reous and magnesian toward the top of the sections, but without 

 any defined breaks in the sedimentation. In the medial and 

 upper portions of the sections the magnesian and limestone 

 strata assume great thickness and purity, and are separated by 

 alternations of laminated, calcareous, and magnesian clays, as 

 l)eautifully shown in the bluff's of Mount Bonnel, on the Colo- 

 rado river, northwest of Austin. :]; 



*Loc. cit., pp. 205-300; also First Annual Report of Texas Geological 

 Survey for 188'J, 1890, p. Ixxxv. 



t Am. Journ. Sci., vol. xxxiu, April, 1887, p. 2!)8. 



j: Photographs of the scenery and structure of the Cretaceous forma- 

 tions of Texas, made by the writer for the Texas State Geological Survey, 

 can be procured from' the Committee on Photographs of the Geological 

 Society of Anaerica. 



