74 GULF TERTIARY OF TEXAS. 



rence of glauconite fossil impressions in the iron ore. A large supply of iron 

 pyrites is also found in a thin bed of sand and clay containing large quanti- 

 ties of, and often entirely composed of, that mineral, with small pieces and 

 seams of lignite, and directly overlying the glauconite. The following sec- 

 tion shows its occurrence in a pit at McBee School, two miles east of Alto, 

 Cherokee County: 



1. White sandy clay 10 to 30 feet. 



2. Ferruginous sandy clay becoming stony hard at the base 1 foot. 



3. "White siliceous sandstone with a cement of finely disseminated iron pyrites . . 1 to 3 in. 



4. Loose sand with lenticular masses of lignite, one to four inches thick, and 



many disseminated particles of iron pyrites, running into a very plastic 



dark greenish-brown clay below 3 feet. 



5. Dark green glauconitic marl with casts of fossils, at bottom of the pit. 



Here we doubtless have the original condition of the strata above and be- 

 low the iron ore horizon before the brown hematite was formed. It will be 

 seen that the brown hematite is not represented in the section, but in its place, 

 i. e., below the top of the sandy clay and above the greensand, are some four 

 feet of clay and sand, with large quantities of iron pyrites. There is enough 

 of this mineral here to give rise to a bed of brown hematite ore equal in 

 thickness to the average of that found in the country, without the assistant 

 supply from the glauconite. The ferruginous matter from the decomposition 

 of the pyrites would percolate into the black clay and with it form the brown 

 hematite as it now occurs. The clay would supply alumina to the ore, and 

 hence the source of that material found in all analyses. Also, the ore fre- 

 quently contains inclusions of clay, and the laminae are often coated with a 

 thin film of it, giving rise to a brittle gray colored mass known as " buff- 

 crumbly ore." In fact every material found in the brown hematite is also 

 found in the materials of this section, and the process of decomposition and 

 of subsequent reconstruction in an entirely different form of the substances 

 involved, is simply the fulfilment of the laws of chemistry. The reason that 

 this section is still seen in this almost entirely unchanged state is due to the 

 fact that the overlying sandy clay is a very stiff impervious bed, and has 

 protected the underlying strata from the decomposing influences of the air. 

 But that even in spite of this protection it is beginning to decompose, is seen 

 by the ferruginous crust at the base of 2 in the section. Also by the 

 fact that a spring, heavily charged with iron, rises from it. This fact also 

 gives a reason for the local absence of the ore, even in the iron ore belt, where 

 the capping of sand is very heavy or very clayey, as this protects the iron 

 pyrites from decomposition, and hence prevents the formation of the brown 

 hematite. Another cause for this absence of the hematite is also to be found 

 in the very probable local absence of the pyrites, even in the midst of pyrit- 



