70 GULF TERTIARY OF TEXAS. 



on Gent Mountain and elsewhere. The range is of the customary plateau 

 character, is twelve miles long, and varies in width from a hundred yards to 

 a half mile. The sand cap overlying the iron here is much thinner than on 

 many of the other iron-bearing ranges, and often the bare ore bed is exposed 

 directly on the surface of the ground, thus adding greatly to the value of the 

 deposit, as the mining of it requires but little or no stripping. The absence 

 of this covering is doubtless due to the narrowness of the range, which has 

 made it easy work for the surface waters to wash away the loose sand, and 

 also to a westerly dip of the iron ore, which has still farther facilitated the 

 erosion of the surface deposits, by allowing the superficial waters to run oft' 

 at a rapid rate, and all in one direction. This westerly dip is peculiar to this 

 plateau, and extends along it throughout its whole length. It is doubtless 

 due to a local sinking to the west of the underlying strata, probably before the 

 formation of the iron ore, and also before the plateau was cut out of the Ter- 

 tiary strata. At Mount Selman, eight miles north of Jacksonville, the ore on 

 the eastern brink of the range is seventy feet higher than it is on the western 

 side, less than one mile distant. Another result of this dip is to make the 

 eastern slope of the range very steep, and in some places perpendicular, while 

 the western slope drops off much more gradually toward Gum Creek bottom. 

 Mount Selman is simply a part of this range, and the village of that name is 

 situated directly on the summit of the plateau. To the north of it the ore ex- 

 tends for four miles, and reaches its terminus at a point one mile south of the 

 Smith County line, and a little greater distance southeast of the village of 

 Bullard. Here the range ends in a small flat-topped hill a hundred yards 

 long by ten to thirty yards wide. To the north from here the country slopes 

 off gradually to Tyler, in Smith County, in a stretch of fertile country with 

 red and mulatto soils, and largely underlaid by glauconiferous strata. The 

 Kansas and Gulf Short Line follows the crest of this ridge from below Bul- 

 lard to within three miles of Jacksonville. In a cut on this road about a 

 mile and a half south of Mount Selman is seen a somewhat unusual occur- 

 rence of iron ore. It consists of large concretionary masses six to seven feet 

 in diameter, of a black or dark rusty-brown color, and imbedded in the in- 

 durated altered greensand. This is overlaid by the regular horizontal bed of 

 ore, as shown in Fig. 5, Plate II. 



The origin of these masses will be explained on page 73. A short dis- 

 tance south of this is McKee's Gap, which is a narrow break in the top of the 

 plateau and is the only interruption in the continuity of the iron ore through- 

 out its whole twelve miles of extent. The ore. of this area is of very regular 

 thickness, varying from two to three feet. The following section on the 

 eastern slope of the range south of Mount Selman shows the occurrence of 

 the ore: 



