STRATIGRAPHY. 



17 



mations. The strata are rarely exposed in such a way as to show any con- 

 siderable thickness of any beds, and reliable records of well-borings are very 

 scarce. It seems possible, also, that much of the Tertiary area may have 

 grown by a gradual encroachment of the land on the sea by a process of ac- 

 cretion, such as is seen in many places on the Atlantic coast to-day, and that 

 it does not always require the supposition of a submergence.* 



For the sake of convenience in description, the Tertiary strata underlying 

 East Texas have been divided as follows: 



SECTION OF THE GULF 



TERTIARY OF TEXAS. 





Later Tertiary? 



{Grand Gulf, Hilgard): 



Eocexe: 



Fayette Beds. 



Timber Belt or 

 Sabine River 

 Beds. 



Basal, or Wills 

 Point, Clays. 



Sands, clays, and lignites. 



Sands, clays, lignites, and 

 glauconites, or green- 

 sand marls. 



300 to 400 feet. 

 800 to 1000 feet. 



250 to 300 feet. 



Sufficient data have not as yet been collected to warrant an attempt at a 

 detailed correlation of all the Texas Tertiary with that of the other Gulf 

 States, and therefore the various strata are provisionally divided as above. 

 The classification depends, first on their lithological character; and secondly. 

 on the very different and very characteristic topography that each of the 

 three divisions gives to the country underlaid by it. The Basal or Wills 

 Point Clays underlie a narrow strip of rich rolling prairie region, east of and 

 parallel to the great Cretaceous prairie of Central Texas. The Timber Belt 

 sands and clays underlie the great timber region of East Texas, and the Fay- 

 ette Beds, so called from their extensive development in Fayette County, on 

 the bluffs of the Colorado River, underlie the interior part of the coast prairies. 

 The coastal part of this latter region is occupied by Quaternary deposits, to be 

 treated later. Throughout the whole of the Eocene area no evidence of any 

 considerable break in deposition can be seen. The lagoon and marine de- 

 posits appear to have alternated with each other in an unbroken series. Fre- 

 quently there are found in one bed fragments of the stratum that underlies 

 it, but no great amount of erosion of these lower beds appears to have taken 

 place, and the little that has gone on is simply what might have been ex- 

 pected to accompany a gradual transition from one kind of deposition to an- 

 other. The paleontological evidence on this point, though as yet somewhat 

 meagre, all tends to show a gradual and almost continuous deposition from 

 bottom to top of the series, and the few breaks in the fauna that have been 

 observed can probably all be explained by the interposition between the fos- 

 siliferous beds of the lignitic and other non-marine strata. In this continuity 



* The estimates of thickness given below are simply approximations, and are intended more 



to show the relative size of the different divisions, than to represent absolute thickness. 

 B 



