THE IRON ORES OF EAST TEXAS. 73 



is frequently found without any covering of ore. A comparison of the parts of 

 the bed that carry ore and the parts that do not, discloses the following facts: 

 That the parts carrying ore are yellow, indurated, and partially decomposed 

 for some distance in from the surface; also that though they once contained 

 large quantities of fossil shells, these shells have either entirely or almost en- 

 tirely disappeared and only the casts of the shells remain ; also that when the 

 bed is dug into until the green undecomposed part is reached, large qauntities 

 of undecomposed iron pyrites are seen, the only trace of it on the outside 

 being rusty spots or a hard brown ferruginous crust; also in the sandy clay 

 immediately overlying the greensand there are frequently found large quan- 

 tities of iron pyrites. An examination of the part that does not contain ore, 

 or where the ore is very thin or scattered, discloses the following facts : The 

 greensand preserves its green color often even on the surface, and shows 

 little or none of the tendency to go into a yellow mass seen in the iron regions; 

 also the fossils are represented by the shells themselves, and not by the casts 

 of the same; also little or no iron pyrites is present. The natural conclusion 

 from these facts is that the presence of iron, the removal of shells, the altera- 

 tion of glauconite, and the accompaniment of iron pyrites are closely connected 

 phenomena; and everything goes to show that they are not only closely con- 

 nected, but are absolutely dependent on each other. The explanation seems 

 to be that the change results from the decomposition of iron pyrites. The 

 decomposition of this mineral gives rise to sulphate of iron and sulphuric 

 acid. The sulphate of iron is either carried off in surface waters or decom- 

 posed on the spot into hydrous peroxide, the basis of the iron ore of the 

 region. The sulphuric acid, set free by the decomposition of the pyrites, 

 attacks the fossil shells, which are composed largely of carbornate of lime, 

 and forms carbonic acid and sulphate of lime (gypsum). It also attacks the 

 glauconite, decomposing it either partially or wholly, and converts it into the 

 yellow indurated mass seen everywhere in the iron ore region. In many places, 

 however, iron pyrites has not produced the whole of the iron ore bed, but 

 has been assisted by the decomposition of the glauconite, which itself contains 

 over twenty per cent of metallic iron. When the pyrites is absent this does 

 not decompose easily, but the continued action on it of sulphuric acid, from 

 the decomposition of the pyrites, causes it gradually to break up into its vari- 

 ous constituents. The sulphate of iron resulting from this would, in turn, 

 become decomposed into the hydrous peroxide, which would be deposited 

 with the portion of the same material furnished by the iron pyrites. That 

 the ore is often entirely produced by the pyrites unassisted by the glauconite 

 is proved by the fact that it is often separated from this latter by a clay one 

 to three feet thick; and that the glauconite does sometimes assist is seen in 

 the occasional blending of it with the ore, as well as in the very rare occur- 



