STRATIGRAPHY. 



23 



of subcoastal deposits compose by far the greater part of the series, and the 

 marine strata represent slight and temporary submergences of the coastal area. 



"The Tertiary strata strike in a general northeast and southwest direction, 

 approximately coincident with the coast, and dip gently toward the east or 

 southeast at an angle varying from to 5 degrees. This dip, however, is 

 very irregular and undulating, and no estimates of thickness of strata based 

 on it can be relied on. In fact, a northerly or northeasterly dip is of no un- 

 common occurrence, though it is simply a local phenomenon. 



"This variable character of the dip, however, does not require the suppo- 

 sition of a disturbance or upheaval of the strata for its explanation. It is 

 doubtless due to the natural sinking and warping in a great thickness of soft 

 beds. In fact, it would seem a most unnatural thing to see several hundred 

 feet of soft clays and sands, covering an area of many thousand square miles, 

 lie horizontally when they were exposed to the influence of atmospheric 

 agencies. The unequal expansion and contraction of strata of different con- 

 stituents, due not only to heat but to the drying out of the beds, would alone 

 account for much or all of the warping that is exhibited throughout the 

 Tertiary country. Besides, the chemical action that has gone on in these 

 beds is probably also accountable for a part of the variable dip. Faults are 

 of frequent occurrence, and are to be accounted for on the same principle as 

 the variations of dip. They are rarely over eight or ten feet in throw, and 

 play no important part in the features of the country. Jointing is also a very 

 common phenomenon throughout the whole of the East Texas region. 



" Estimations of thickness of the Tertiary strata of this region are attended 

 by peculiar difficulties, as the dip is too variable to be relied on in such esti- 

 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 underly- 

 ing East Texas have been divided as follows: 



SECTION OF THE GULF TERTIARY OF TEXAS. 



Later Tertiary? 



(Grand Gulf, Hilgard): 



Eocene : 



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. 



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

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



