22 THE IRON ORE DISTRICT OF EAST TEXAS. 



tured the country into its present contours; the fall and rush of surface waters 

 wearing away the exposed beds of sands and clays; the springs by their slower 

 but more continuous action performing the part of sub-erosion, and undermin- 

 ing and breaking down many hills and plateaus that would otherwise stand 

 unimpaired on account of their more impervious coverings. 



This region is heavily timbered. On the south is the terminus of the long 

 leaf pine belt of the South Atlantic and Gulf States, which to the north gives 

 way to the short leaf pine, the oak, the gum, and the hickory. 



STRATIGRAPHY. 



The iron ore region of East Texas, as here denned, is underlaid for the 

 most part by strata of Tertiary age. In only a few places are there exposures 

 of Cretaceous strata, and when they do appear as inliers they belong to its 

 uppermost members, and are accompanied by salines. 



"The uppermost part of the Cretaceous and the base of the Tertiary strata 

 are both composed of soft clay and sand beds, which succumb readily to the 

 weathering action of the atmosphere, and consequently the line of separation 

 is often impossible to locate exactly. The uppermost beds of the Cretaceous 

 in Texas and Arkansas' are composed of sandy and 'glauconiferous' strata, 

 sometimes reaching a maximum thickness of three hundred feet. These have 

 been termed the ' glauconitic ' division by Hill. They vary in composition 

 from beds of pure siliceous sand to beds composed entirely of glauconite, and 

 between these two extremes are found all gradations in the relative propor- 

 tions of the two materials. These beds are the equivalent of the Ripley 

 Division of Alabama, and probably are the Southern representative of the 

 'Fox Hills' Beds of Nebraska. The 'glauconitic' deposit becomes more 

 argillaceous towards its base, and gradually runs into a great deposit of cal- 

 careous clay over twelve hundred feet thick, and characterized by large quan- 

 tities of Exogyra ponderosa. This bed represents the ' Exogyra Ponderosa 

 Marls' of Hill's Upper Cretaceous section, and underlies a large part of the 

 great prairie region of Central Texas. These Upper Cretaceous beds dip 

 gently to the south and southeast, and formed the Texas shore line of the early 

 Tertiary sea. Upon their much eroded surfaces were deposited the Eocene 

 clay and sandy strata which underlie East Texas. 



"The Tertiary deposits of East Texas, overlying these Cretaceous strata, 

 consist of a vast thickness of sand, clay, and glauconite beds, in some places 

 characterized by great quantities of lignite, and in others by beds of littoral 

 fossils. In fact the whole series represents a succession of coastal, subcoastal, 

 or brackish water deposits, alternating with marine deposits of a littoral char- 

 acter, and between these two extremes we find all gradations. The lagoon 



