iron. 613 



morphosed Texian marbles and graphitic rocks with the similar Fernandian 

 types. A little observation will teach the differences, which can often be 

 determined by the discordant trends, although this is not a safe guide over 

 extended areas. The difficulty may be almost wholly avoided by keeping in 

 mind the fact that the Fernandian graphite is schistose rather than slaty, and 

 that the Fernandian marbles are usually blue, while the Texian System in- 

 cludes those which are white and yellow. The marbles of both systems are 

 crystalline dolomites, not amorphous beds like the ''Burnet marbles" or " lith- 

 ographic stone " of later origin. 



The magnetites, strictly speaking, are confined to the Fernandian System. 

 Upon the Economic Map the courses and positions of the bands are accu- 

 rately placed, and in a general way the locations are shown where there is 

 any reasonable prospect of discovering workable deposits. It will be noticed 

 that the belts are interrupted in places. This is due to the absence in those 

 spots of the iron bearing series or to its being buried beneath later strata. 

 The former condition prevails in those areas in which other characters are 

 depicted upon the map, and the covered areas are left blank or are traversed 

 by bands of the vein ores which have been derived from the buried exten- 

 sions of the hard ore bands. Whenever the Fernandian strata are the sur- 

 face terrane the chances for the discovery of good bodies of Bessemer ore are 

 very favorable, provided that search is made in the course of the hard ore 

 bands, as shown on the Economic Map herewith. I have plotted these bands 

 in some cases where they may not exist, in order to show their courses through 

 the interior area, and because there are certain places where it is possible that 

 local patches of Fernandian rocks may have escaped notice in my survey of 

 the region. 



The analyses made by the chemists of the Survey of my samples, as re- 

 ported in Table III, give a very clear notion of the general run of these ores. 

 Below are given some of the distinguishing features of the separate bands, 

 although there is a close resemblance among them all, as might be inferred 

 from the structure. It should also be premised that the nearly vertical posi- 

 tion of the beds in the Iron Mountain and other bands is not a necessary 

 concomitant; and it may well happen that in some areas the low inclination 

 of the iron stratum may make it profitable to work it over somewhat wider 

 tracts than in those particular fields. An accurate section across the area in 

 any one line must fail to express the situation so that it may be readily un- 

 derstood, and the complication is so great that it is not safe to make strati- 

 graphic generalizations to be used as guides in practical work. 



For the benefit of prospectors and those engaged in mining exploration, 

 the following hints are reproduced from the writer's 1889 Report: 

 47— geoi. 



