Geology of the Trinity Country^ Texas. 211 



Art. II. — Observations on the Geology of the Trinity Country, 

 Texas, made during afi excursion there in April and May, 

 1839. By J. L. Riddell, M. D., Professor of Chemistry in 

 the Medical College of Louisiana. 



It is well known that, as you proceed inland from the Gulf of 

 Mexico in Eastern Texas, to the distance of eighty or ninety 

 miles, the face of the country presents a general plain, almost as 

 level as the surface of the ocean. As it is elevated thirty or forty 

 feet above tide water, it is necessarily furrowed by water courses ; 

 but its most remarkable feature where prairies prevail is the exis- 

 tence of multitudes of wet places, each covering from a few roods 

 to. an acre or two in extent, and having a depression of one or two 

 feet below the general level ; while always around the margins 

 of these low places are several rounded mounds, having a base of 

 ten or twelve feet, and a height perhaps one fourth as great. 



Compared with the age of the main American continent, all 

 this land may be considered as having quite recently emerged 

 from the dominion of the sea. It is essentially a vast deposit of 

 sea sand, so completely identical in all its characters with the 

 sands of the present shores and shallows of the gulf, that its ori- 

 gin cannot well be mistaken. Occasionally it embraces extensive 

 beds of a red earthy marl. For instance, this marl may be seen 

 in great abundance where excavations have been made for con- 

 structing a road in the bank, near a hundred yards northwest of 

 the steamboat landing at Houston. By chemical examination I 

 find a sample of this marl to consist mainly of carbonate of lime, 

 red oxide of iron and silex. I believe it may be found of incal- 

 culable value to the city of Houston, and to the whole country 

 above alluded to, inasmuch as limestone is not therein known to 

 occur. 



This marl, if calcined after the manner of burning hme, will be- 

 come converted into a very good quicklime, of a reddish brown col- 

 or. Nothing can be more efficient as the calcareous ingredient in 

 all kinds of mortar, for laying bricks, making underground water 

 tanks, and plastering houses internally and externally, where the 

 color is no objection to its use. In fact it might be universally 

 substituted for white lime, the iron or coloring material having 

 only the effect to render it more hard and enduring than it other- 

 wise would be. 



