84 A GEOLOGICAL SCBVET OF LAXDS 



The lignite seams which have been found in the clays aboA^e 

 the main waters and in wells made west of Carizzo Springs,, and in 

 the region of the Wilderness Lake and the Beef Hollow pastures 

 are apt to have a less variable development, for they were formed 

 in the Tertiary coastal waters at a time when the shoreline was 

 more distant and when the lagoons were more extensive and 

 uniform in their physical features. The upper lignite beds con- 

 tain the productive deposits, but they are not productive in every 

 locality. In Zavalla and Dimmit counties the beds to which they 

 belong do not extend farther west than to within six miles of 

 Maverick county, and usually they do not extend that far west. 

 So far as I could learn, nothing is known of these lignites on the 

 Company's lands except from explorations made by churn drills, 

 and no reliable estimates on the thickness of such seams can be 

 made except by the use of core drills. In Webb county these clays 

 underlie the east part of block 7 and all of blocks 8 and 14. It is 

 not likely that lignite beds of this horizon anywhere lie deeper 

 than 400 or 500 feet on any of the Company's lands west of the 

 Xueces river. A vein reported to be three feet thick was found in 

 a well made on the Trinidad Sanches survey at a depth of 75 feet. 



PLEISTOCENE DEPOSITS. 



The surface of the uplands in the upper part of the Eio Grande 

 embayment sometimes consists of the bare outcrops of the coun- 

 try rock, with thin patches of scanty soil. More frequently the 

 bed rock is covered by a continuous thin land drift with a mantle 

 of dark soil. In a few places this land drift rests on sediments 

 which are evidently much later than the early Tertiary rocks just 

 described. The springs on Tequesquite creek, four miles above its 

 mouth, issue from such a deposit. Its lower partis acoarse gravel 

 which changes upward into cross bedded sand and then to clays 

 and fine sands of yellow color. These gravels and sands are prob- 

 ably not very extensive, but they are clearly the cause of the 

 springs, which result from a slow seepage of water retained and 

 stored in the porous sand. 



Material unlike this, but of nearly the same age, forms a verti- 

 cal bluff on the east side of a creek known as Agua de Fuera at a 

 point a mile and a half northeast of Spofford. It rests on clay 

 and stonv ledges of the Austin chalk. Below it consist of a con- 



