li. T. Hill — Deep Artesian Boring in Texas. 409 



been pointed out by Penrose, but no satisfactory interpreta- 

 tion has been made of its limitations and history. As shown 

 by Shuinard* and Copef it contains the wonderful mam 

 malian vertebrate fauna of the Loup Fork and Equus beds 

 which are supposed to be of Miocene and Pliocene age. Its 

 sediments are identical in many unique characters with those 

 of the formations I have seen in Nebraska and on the Staked 

 Plains containing besides the same vertebrate remains the 

 peculiar opalized wood and quartz grains imbedded in a lime 

 matrix identical with the mortar beds of Kansas described by 

 Hay. It is evidently the coastward extension of the Great 

 Plains formation which, as I have shown, extends over the 

 whole Llano Estacado to the Rio Grande:}: as far as Spofiord 

 Junction. Whether this formation was deposited at marine 

 base-level or was laid down upon the land after the manner of 

 deposition now going on so extensively over the arid region of 

 Mexico is an interesting problem. One fact is positive, how- 

 ever, and that is that it represents a period of great aridity 

 which prevailed in Miocene and Pliocene time throughout the 

 region of its occurrence. 



These three sheets of sedimentation, representing 827 feet 

 of Pleistocene beds, 927 feet of later Tertiary — Miocene and 

 Pliocene — and 2000 feet of Eocene 'deposits reveal a great 

 load upon the coastal plain, and each, according to the doc- 

 trine of isostasy, would afford a sufficient factor to account for 

 the important movements of their respective epochs. 



Could the well go deeper into the 2500 feet of Upper Cre- 

 taceous chalks and clays and the 2500 feet of Comanche 

 deposits the total load upon the Gulf's margin since the sea 

 first began its oscillations over the Texas region in Wealden 

 time would amount to 8000 feet. 



The oldest and latest of the three divisions into which I 

 have divided the section, the Eocene and Columbian respec- 

 tively, were deposited in very shallow water under conditions 

 identical with the sedimentation of to-day, while the middle 

 division no doubt represents even as shallow if not shallower 

 deposits but under entirely different climatic conditions. All 

 must represent subsidence, although there were no doubt 

 intervening periods of elevation which can only be interpreted 

 upon the land, according to the methods of the modern school 

 of physical geologists. The total subsidence of the old Eocene 

 shore line, according to this boring has amounted to nearly 

 three thousand feet. 



*Trans. St. Louis Academy of Science, vol. ii, 1868, pp. 140-141. 

 •{■Various papers of Professor E. D. Cope. 



X Occurrence of Underground Water in the Texas New Mexican Region. 

 Washington, D. C, 1892. 



