iron. 625 



they will ordinarily, but perhaps not always, be better in the northwest trend 

 than in the northeastern course, and that the regularity of the veins is apt to 

 be less disturbed in their path through the compact Silurian limestones than 

 along the line of their passage through the porous Cambrian sandstones. 



In the analyses of typical samples reported in Table III the " loss by igni- 

 tion " does not, of course, represent the exact proportion of water in all cases, 

 but the general relations of the ores may be understood by reference to that 

 column. Turgtte, goethite, and Umonite are the prevailing types, some very 

 fine radiated examples of turgite occurring near the divide between Hinton 

 Creek and Deep Creek on the Fredonia and San Saba road. In fact it is 

 necessary to draw arbitrary lines, owing to mixtures of the principal minerals 

 in the ores. Some of these veins have been worked by persons who have 

 believed them to be rich silver ores. No. 61, Table III, is an example from 

 one of these prospects. As will be seen by the analysis, it is a very good 

 limonitic iron ore, but with rather a high percentage of phosphorus, due no 

 doubt to its proximity to the greensand beds of the Potsdam Series. 



The limonites may become important sources of revenue in addition to the 

 other iron ores, although they are not always abundant enough to sustain any 

 metallurgic industry by themselves. In some cases, however, as at the 

 Chaney diggings, southeast of Packsaddle Mountain, the quantity is sufficient 

 for profitable working, and the prospect for better ore (manganese or iron) 

 below is very good when the structure is considered. The same remarks 

 apply to veins near Camp San Saba, on Long Mountain, Llano County, in 

 southwestern Burnet County, and elsewhere. There are many localities in 

 the Silurian and Cambrian rocks where veins of this kind outcrop, especially 

 in the San Saba River valley. 



The lines indicated upon the Economic Map are mostly the actual courses 

 of veins ascertained by a multitude of observations in the field. While they 

 have in no sense been drawn to fit the theory of intimate connection in dis- 

 tribution with the basal magnetites, it will be seen that they confirm that idea 

 in a most remarkable manner. 



I have mapped the veins as far as practicable to the outer edges of my dis- 

 trict, where they appear to pass beneath the post Silurian strata. Where the 

 Devonian, Carboniferous, or Cretaceous strata overlie the prolongations, the 

 lodes are buried beneath them, I presume, although this inference is of 

 course not based upon extensive examinations of those terranes, which have 

 been assigned for study to other members of the Survey. Mr. Cummins 

 confirms my opinion by informing me that such veins do not appear in the 

 Carboniferous rocks of his district, and they have not been reported, to my 

 knowledge, in the Cretaceous System. I have not observed them in any out- 

 crops of either system which have been passed over by my field parties. 



