92 PROCEEDINGS OF WASHINGTON MEETING. 



continuation, the western margin of the main Grand prairie, have suffered is enor- 

 mous, for it together with the former westward extent of the upper Cretaceous and 

 Eocene and the eastward continuation of the Llano Estacadohave been removed in 

 Neocene time from almost all of the central denuded <>r Paleozoic region of Texas — 

 a simple and evident fact, yet so large and profound as imt to have been recognized 

 by local geologists. This denuded material has all entered into the structure of the 

 Coast and Fayette prairies, the material and vast extent of which alone, if topo- 

 graphic proof were lacking, would he sufficient to demonstrate the great denudation. 

 The genesis of this vast plain, the Llano Estacado and Edwards plateau, has long 

 puzzled me, for 1 have tried to make it harmonize with the lacustral doctrine by 

 which its northern extension in Nebraska and Dakota has been explained. Tins 

 lacustral doctrine, as applied to the Laramie and other post-Cretaceous phenomena 

 of the west, necessitates a hypothetic land harrier between the eastern escarpment 

 of these plains and the coast in an area now actually occupied hy valleys of ero- 

 sion, and without any evidence whatever, structurally or otherwise. Thanks to 

 the investigations and direct suggestion of 'Mr. McGee, I am now inclined to con- 

 sider it the interior margin of a great littoral sheet of deposits which extend to the 

 Gulf. Although this hypothesis involves the erosion in post-Tertiary time of 

 nearly 200,000 square miles of area, it is sustained by three important lines of evi- 

 dence : 



1. The great land stripping at presenl going on in the central region, and the 

 eastward succession of the scarps of the series of the coastward incline. 



2. The deep incision by the older rivers of this coastal plain, the Brazos and the 

 Colorado having cut 1,000 feet below it. 



."!. The actual remnants of the plain over the denuded area, occupyingthe divides 

 of the drainage. 



4. The existence beneath the coastal clays in eastern Texas of a great formation, 

 tion, which may prove a continuation of the Llano Estacado sheet. 



The Washington Praikies. 



Immediately westward of the coastal prairies (which it will be remembered are 

 composed of unconsolidated clays) there is another region, of which the chief 

 characteristic is a rich, black, sandy soil, derived from the disintegration of a friable 

 sandstone, composed largely of well rounded and polished grains of quartz cemented 

 by a white calcareous matrix — a great water-bearing formation which dips beneath 

 the coast clays and supplies the artesian waters of that region. 



These prairies have been mapped out by Dr. R. II. Loughridge, and the underlying 

 formation has been described by Roemer, Shumard, and Penrose, the latter propos- 

 ing for it the name of Fayette sands. 



These sands have a remarkable resemblance to the deposits constituting the Llano 

 Estacado formation, and contain also the peculiar opalized wood and fossil hones 

 and leaves characteristic of that formation, and it is probable that they are the 

 same or a closely allied terrane which once extended continuously over the entire 

 region ; and I am also inclined to believe, with Shumard and Roemer. that they are 

 of Miocene or Pliocene age, rather than Quaternary, as asserted in the Report of 

 the Texas Survey. 



Dr. P>. F. Shumard, in 1861, correlated this formation with the great plains and 

 announced* " the discovery, in Washington and adjoining counties, of an extensive 



*Trans. St. Louis Academy of Science, vol. -i. L868, pp. I la Ml. 

 t 



