354 CENTRAL MINERAL REGION OF^TEXAS. 



and other qualities. A close examination of these will make it clear that 

 they contain a certain amount of disseminated magnetite, which fact ex- 

 plains the occurrence of the iron protoxide. Others are slightly hydrated, 

 amorphous, and generally similar to limonite, but with the color and streak of 

 hematite, and giving its blow-pipe reactions. Careful observation and de- 

 tailed study of the occurrences of the different varieties prove that this 

 gradation of the hematites both ways into the other classes is not merely hy- 

 pothetical, but that sharp lines are not drawn in the actual outcrops where 

 the different types occur together. The transition is real, not fanciful. 



Beds of hematite in our district are unusual, excepting where they occur 

 with the magnetites, as previously explained. This mineral occurs here under 

 somewhat diverse conditions, but it has not yet been observed in any situa- 

 tion where its relations are such as to imply an independent origin. So far 

 as known it is with us a secondary deposit — a derivative from the subjacent 

 magnetite, directly or indirectly. Sometimes it occurs in a way to suggest 

 the reverse alteration from limonite, but such cases are comparatively rare. 

 There are also special inclusions in certain veins of quartz, but these are not 

 now under review. 



The outcrops of this class of ores along portions of the northern border of 

 the magnetite area are chiefly segregations in Cambrian sandstone, occurring 

 as black or blood-red impregnations, varying in quantity from simple colora- 

 tion and cementation to thin streaks, ramifying seams, and even solid strata 

 of noticeable thickness. In some places erosion has cut off the sandstone in 

 such a manner as to leave low escarpments of the iron-bearing sandstone, 

 and this has given rise to the erroneous idea that there is an east-west strike 

 to these deposits. There is certainly a wide field for inquiry concerning the 

 history of deposition of the hematites, but enough has been learned to explain 

 fairly the common methods of occurence. Three different kinds of exposures 

 may be made out as viewed with reference to their modes of origin. To these, 

 for convenience, we may give names as follows: (1) Altered Magnetites; (2) 

 Concretionary Ores^ and (3) Hematite Sandstones. Such a classification does not 

 exhaust the variety due to local and special causes, but it gives a sufficiently 

 accurate arrangement for a preliminary discussion. 



(1) THE ALTERED MAGNETITES. 



A very common experience in our district is the observation by travelers 

 of large amounts of what may be termed "iron float" in pebbles, boulders, 

 and apparent strata. These occur at intervals in various parts of the region, 

 but especially at or near the contact of the red Cambrian sandstones with the 

 Fernandan strata, along the borders of the magnetite area previously defined. 

 To the novice there is not much difference in the material at sight, but almost 



