76 GULF TERTIARY OF TEXAS. 



found in the interior of the glauconite bed, and the principle of their forma- 

 tion is doubtless similar to that already described, by the decomposition of 

 iron pyrites, often assisted by glauconite. 



2. NODULAR OR GEODE ORES. 



These ores, though somewhat similar in chemical composition, are distinctly 

 different in physical character and in their mode of occurrence from those 

 already described. They are well developed in the northern part of Marion 

 County and in southern Cass County, and extend thence into Morris, Camp, 

 Upshur, and the counties lying to the west. 



The ore is a brown hematite and occurs in a great variety of forms. It 

 very rarely shows the laminated structure of the brown laminated ores or 

 their resinous lustre. It generally occurs as nodules or geodes, or as honey- 

 combed, botryoidal, stalactitic, and mammillary masses. It is rusty brown, 

 yellow, dull red, or even black in color, and has a glossy, dull, or earthy 

 lustre. The most characteristic feature of the ore is the nodular or geode 

 form in which it occurs. Some of the beds are made up of these masses, 

 either loose in a sandy clay matrix or solidified in a bed by a ferruginous 

 cement. The ore lies horizontally at or near the tops of the hills, in the same 

 manner as the brown laminated ores to the south of the Sabine River. The 

 beds vary in thickness from less than one foot to over ten feet, the thicker 

 ones being often interbedded with thin seams of sand. The ore-bearing beds 

 are immediately overlaid by sandy or sandy clayey strata. The sand beds 

 are in the majority, though pure clay is found at some distance below the 

 ore. The overlying sands are at times entirely eroded and the solid floor of 

 brown hematite is exposed to view. In other places it is covered by from 

 one to thirty feet or more of sand. This overlying stratum varies consider- 

 ably in character; sometimes the sands are loose and gray, at others more or 

 less solidified and deeply stained by iron. Sometimes they contain consider- 

 able clay and show ferruginous segregations, so that a section of the bed 

 discloses lumps of hard, yellow semi-hardened sandy clay. The beds also 

 often have a mottled red, yellow, and white appearance, and contain thin 

 seams and lumps of clay. The sands are very much cross-bedded, and fre- 

 quently layers of hard-pan or thin ore are seen following the lines of cross- 

 bedding. Unlike the ores of Cherokee, these beds are not dependent on the 

 thickness of the immediately overlying sands. 



Sometimes, though not so often as in Cherokee County, the ore is capped 

 by a stratum of hard ferruginous sandstone* varying from one inch to over 

 a foot in thickness, and occasionally similar beds are interstratified with the 



* Frequently this sandstone is found alone and without any ore. In such cases it some- 

 times reaches a thickness of over twenty feet. (See Building Stones.) 



