624 CENTRAL MINERAL REGION OF TEXAS. 



The great bulk of the material is hematite, as shown by the blood red 

 streak and powder, but analyses ordinarily yield small percentages of water. 

 It does not necessarily occur in concretions with concentric layers, although 

 such are abundant at times, but there is very commonly a nodular weather- 

 ing. Occasionally, however, the ore forms encrusting shells or plates inter- 

 lacing or ramifying through the substance of the sandstones. There are also 

 instances of the enlargement of the streaks until they reach a very consider- 

 able thickness and weather out from the containing rock in masses which 

 closely simulate fragments from the original band ores. This last mode of 

 occurrence is particularly evident in some of the deposits on and near Elm 

 Creek, north of east from Castell. 



The concretionary ores may perhaps have been themselves subjected to a 

 process of solution and resegregation in some instances, and in other places 

 they have no doubt contributed their quota to the degrading action which 

 has produced the later and less valuable ores of the sandy type. Many of 

 the Cambrian sandstones, especially of the Middle Series, are merely ce- 

 mented or even only colored by these mild impregnations, and these effects 

 are usually restricted in distribution. 



4. SOFT (VEIN) ORES. 



The hydrated ores, commonly known as limonites, are more abundant than 

 was at first supposed in examining the resources of the Central Mineral Re- 

 gion. As remarked in the Report for 1889, page 359: 



Aside from the insignificant quantity which comes in as contaminations through altera- 

 tions of the anhydrous ores, these hydrous oxides appear almost exclusively in veins, for the 

 most part in the older rocks. The most important fact connected with their distribution is 

 their occurrence largely in places where there is every reason to believe they are connected 

 with the buried magnetic ores. They often pursue courses more closely related to the Fer- 

 nandian trend than to the principal fault lines at surface in the areas where they outcrop, 

 and where they do not follow this law there is usually an irregular development of the veins 

 which roughly corresponds with the distribution of the magnetites in belts beneath them. 



The Economic Map presented with this Report clearly illustrates this fea- 

 ture, which is in a large measure caused by the northwest-southeast fractures 

 in the Silurian and Cambrian strata, these following almost exactly the 

 courses of the buried hard ore bands. There is also the more characteristic 

 Silurian coarse of fractures (north 25° east) which has its veins of limonitic 

 material. Owing to the variety of the rocks traversed by the veins in depth, 

 and the influence of the sedimentary wall rocks, there is no recognizable 

 standard of vein deposition in this class of ores. It may be predicted that 

 those richest in iron will be most likely to be found where the magnetite 

 bands marked upon the map pass beneath the Cambro- Silurian section; that 



