BENCHES. 85 



from three to ten feet. As has been stated by the writer, in a previous re- 

 port,* these benches can be formed in three different ways: 



1. By landslides, which have carried down a portion of the top bed to a lower 



level, often giving the appearance of a second bed of iron ore, when it 

 is only the edge of the upper one. 



2. The alternation of hard and soft strata. The softer beds become eroded, 



and expose the harder iron ore, sandstone, or hard-pan. 



3. By erosion in successive periods of elevation of the country. 



It is probable that each of these causes has formed some of the benches, 

 but they are usually so heavily covered by detritus that it is often very dim- 

 cult to determine which has formed any certain bench. In the iron ore re- 

 gion of Cherokee, Anderson, and Smith counties, however, they are very 

 often, if not most often, due to landslides. At first it might appear that the 

 great number of such benches on a hill side, their occasional regularity, and 

 their universal occurrence could not be accounted for by this explanation, 

 but an examination of the form of erosion now going on in the country tends 

 strongly to prove that this cause has operated, at least in a great number of 

 cases. As we go over any of the iron- bearing highlands the ore bed is seen to 

 be sunken as we near the brink of the hill, and this is especially true at the 

 heads of ravines where springs gush out. It has already been stated that 

 the iron ore is overlaid by sand and underlaid by a bed of greensand thirty 

 to forty feet thick. Beneath this are interbedded sands and clays, all lying 

 horizontally, or almost so. The springs rise sometimes above the iron ore 

 bed, but more often between it and the greensand, and below the greensand. 

 When the underground waters reach the outcrop of the bed along which 

 they are flowing they appear as a spring, generally highly ferruginous, and 

 giving rise to a small stream. In wet weather the flow from these springs is 

 very strong, and besides carrying out the mineral matter in solution, they 

 also transport in the state of mechanical suspension large quantities of sand 

 from the beds through which the water has flowed before reaching the sur- 

 face. This action gradually makes the sand strata porous and honeycombed, 

 and the result is that it finally reaches such a stage of this condition that it 

 gives way to the pressure of the overlying beds, sinks down, and causes the 

 formation of a bench on the hill side. Of course more sand is carried from 

 the part of the bed near its outcrop than back in the hill, and hence the 

 reason that the benches generally slope toward the drop of the mountain, and 

 also the reason of the downward slope of the ore on the edge of the summit. 



There are many facts that tend to prove that such an occurrence as this 

 has gone on. 



* Texas Geological and Mineralogical Survey. First Report of Progress, 1888, page 55. 



