26 THE IRON OEE DISTRICT OF EAST TEXAS. 



however, are greatly in the minority, and the siliceous sands compose by far 

 the larger part of the whole series. Lignite beds are of very frequent oc- 

 currence, varying from a few inches to ten and twelve feet thick; and the 

 sands and clays are often impregnated with vegetal matter to such an ex- 

 tent that numerous traces of petroleum, asphalt, and natural gas have been 

 found in the East Texas region, sometimes in quantities of considerable eco- 

 nomic importance. Many of the black and brown clays and sands owe their 

 coloring matter to this ingredient of vegetable material, and burn white or 

 buff color when exposed to heat. The sands are generally much cross- 

 bedded, gray to buff in color, and contain black specks, which are often 

 glauconite. This latter mineral is a common constituent in many of the beds, 

 and there are found all gradations, from a pure siliceous sand to a pure green- 

 sand bed, such as are well developed in the iron ore regions of Anderson, 

 Cherokee, Rusk, and other counties. All the sand beds are more or less im- 

 pregnated with carbonate of lime, and often it is in such quantities as to 

 form beds of calcareous sandstone, where it acts as a cement and forms a 

 soft, friable rock. Sometimes even beds of limestone are found, and cal- 

 careous nodules and concretions are of very frequent occurren.ce throughout 

 the whole of the Timber Belt Beds. One of the most characteristic features 

 of the region depends on this presence of carbonate of lime in the sandy beds. 

 It is the occurrence of great masses of sand, varying from one to ten feet and 

 more in diameter, and cemented into a hard rock by the calcareous matter. 

 These rocks vary much in shape and hardness. Sometimes they have a con- 

 cretionary shape and weather in concentric layers; at others they show the 

 horizontal stratification of the beds in which they occur, and gradually blend 

 into the soft enclosing sand. 



"This presence of carbonate of lime is of the greatest importance, from an 

 agricultural point of view, to the welfare of East Texas, as it renders soils 

 underlaid by such strata of great fertility and durability; whereas without it, 

 many of them would be perfectly barren. Many of the sands are also inti- 

 mately mixed with a fine impalpable white clay, which renders the beds soft 

 and highly plastic when wet, but when dry it forms a hard, solid mass, often 

 occurring as a friable sandstone. When such beds are exposed to erosion by 

 creeks and in gullies they break up into lumps, which become rolled and 

 rounded, and form putty-like pebbles. This is a very characteristic kind of 

 erosion in some of the Lower Tertiary strata, and such beds are well devel- 

 oped in central Van Zandt County. The sand beds are generally also varia- 

 ble in composition. They blend by insensible gradations, both vertically and 

 laterally, into clay or sandy clay beds, so that minute correlations, even in 

 beds very close to each other, are difficult to make. This extreme variability 

 in composition is simply one of the many proofs of a near shore deposit. The 



