320 PROCEEDINGS OF THE ACADEMY OF [1893. 



ject may well be stated here before taking up the detailed study. 

 With a few exceptions this study is of necessity confined to east and 

 central Texas for the reason that west Texas, or Trans- Pecos Texas, 

 is practically an unknown land. That part which concerns us 

 most at the present time, is the portion elevated during the begin- 

 ning of the formation of the Rocky Mountains as a great plain, 

 chiefly if not entirely Cretaceous covered, and dipping eastward. 

 Upon this the streams have developed, being revived by the Tertiary 

 and Quaternary uplift. They have in places cut through the Cret- 

 aceous covering and, in the Central Denuded Area, have revealed 

 great areas of buried Palaeozoic rocks upon which they are super- 

 imposed. The reason why the streams have cut through to the 

 Palaeozoic at this their most elevated portion is not now definitely 

 certain. It may have been the result of mere chance, or it may be 

 that this region, having a thinner cover than the other region, was 

 first reached, and. being more resisting because relatively elevated 

 and diversified, and consequently a region of excessive denudation, 

 became a center of drainage. Another possibility is that the 

 Palaeozoic Highland was expressed in the Cretaceous sea by a dome- 

 like bulging in the Cretaceous sediments, and consequently was the 

 first land to be made and the first and most rapidly denuded. 

 For a discussion of the subject I refer to my paper on the Cretaceous 

 Covering of the Central Palaeozoic of Texas. 16 



Part II. — Physiographic Description. 

 1. — General. 

 The different geographic units above mentioned exhibit different 

 phenomena and it seems, therefore, best to divide the discussion so 

 as to give each geographic unit a separate consideration. This divi- 

 sion of the subject cannot be adhered to rigidly because the various 

 regions merge one into the other and the physiography of one very 

 often resembles closely that of another. Yet each geographic unit 

 presents unique features and, for this reason, it seems necessary to 

 consider them as units. Moreover it is the only method of treat- 

 ment which seems possible without the introduction of much confu- 

 sion. 



2 — The Quaternary Coastal Prairies. 



(a) Geographic Description. — Of this plain Hill writes, 17 " It is 



16 Am. Geol., Vol. IX, 1892, pp. 169-178. 

 17 Am. Geol., V, p. 11. 



