REPORT OF THE STATE GEOLOGIST. XXIX 



RESULTS. 



t 



A REVIEW OF TEXAS GEOLOGY AS DEVELOPED BY THE WORK OF THE 



SURVEY. 



As a primary fact established by the work of this survey, it may be 

 stated that Texas is a geological centre or focus. Situated as she is at 

 the centre of the southern border of the United States, the converging 

 lines of the geologic formations which mark the eastern ocean and gulf 

 coast, as well as those of the central basin and western mountain sys- 

 tem, all meet within her borders. Here it is that the true relations of 

 each to the other may be best ascertained, and it will require the facts, 

 that will only be brought to light by detailed study of these relations 

 as they do exist here, to properly explain and interpret much that is 

 now in doubt in the regions further north. 



These various converging areas may be said to divide Texas into 

 four districts. 



The first of these, which is a continuation of those formations bor- 

 dering the Gulf shores of the States east of us, comprises that portion 

 of Texas lying between the Gulf coast and the foot of the Grand Prairie 

 region. In no place does the altitude of this broad belt exceed 700 

 feet above the sea level. Beginning at the coast in level prairies, it 

 gradually becomes undulating, and then hilly, until it meets the higher 

 hills which form the scarp bounding it on the north and west. 



From this boundary line to the foot of the Staked Plains is a second 

 district which stretches away to the Rio Grande and Pecos of the south 

 and west. This district may be subdivided into a plateau on the east 

 and south called the Grand Prairie and an interior basin. This also 

 rises gradually towards its western border, and, though containing many 

 hills and mountains, nowhere is there an altitude of over 2500 feet. 

 Within the encircling rocks of more recent deposition, there lies within 

 this district, like an island in the sea, the older nucleus of the Llano or 

 Central Mineral District, which can well claim close relationship with 

 the oldest rocks which have been found upon our continent. 



The Staked Plains, which form the third district, rise from 300 to 

 400 feet higher, and are a part of the great plains which stretch east- 

 ward from the foot of the Rocky Mountains. These plains, while in 

 reality they rise rapidly towards the west, seem almost like a level floor, 



