288 CENTRAL MINERAL REGION OF TEXAS. 



tongue in the valley of the Llano River, in Kimble County. Upon the 

 southern side of the Paleozoic area of - Central Texas there are also good ex- 

 posures in the valley of James River (east bank) and in a few other places. 



I do not yet feel confident enough of the true correlations of the scattered 

 sections to set a sharp line of demarkation between this series and the one 

 above it. There is a point assumed as a parting in the field which may prove 

 to be an easily traceable horizon, but this would be very difficult to define 

 verbally so that no one could mistake it. Many fossils have been collected, 

 and such attention as has been possible to give them thus far has tended to 

 confirm the judgments based upon the stratigraphy. There is the widest 

 variety in the thickness of the beds, owing to the local inequalities left by 

 erosion and subsidence prior to deposition. This makes it very difficult to 

 give a detailed section which will be characteristic. The maximum thick- 

 ness is probably from 300 feet to 400 feet.* 



In general the rocks are sandstones varying in color from light red and 

 shiny black to brown and yellow, and even white. These conditions are very 

 interesting when considered in connection with the locus of formation in each 

 case, for they can usually be explained by reference to the underlying rocks 

 or to the geographic distribution of the color. Dark brown and chocolate 

 beds are most persistent, the white being confined to areas adjacent to the 

 oldest Archaean rocks. " Sand Castle," one and a half miles northeast of Valley 

 Spring, and " Sand Fort," a similar eminence in the upper part of Cold Creek 

 valley, are examples of the latter class, although it is not certain that they 

 belong to the Riley Series, as I now suppose. The view of the Riley Beds in 

 Sandy Pass, as shown in Plate IX, gives a good idea of the cliffs of sandstone 

 outcropping there. Fault lines of two or more trends are prevalent in this 

 region. In the engraving one of these courses is nearly in line with the face 

 of the cliffs, and another cutting it at an angle of sixty degrees comes in at 

 the right. Sandy Creek is following both faults in its course. These breaks 

 are of later date than the Cambrian. The rocks here are the bright red and 

 white variegated soft sandstones, running up into buff calcareous shales above, 

 the section in the lowest part being much like that of Sand Castle and Sand 

 Fort. Above these, in the weird Glen Gap, a little behind the cliff at the 

 right, a capping of different rock occurs. This is the dark brown granular 

 rock already referred to, and in this segregations of limonite and hematite are 

 common, and occasionally enough manganese stain to give them externally a 

 jet black color. Some compact chocolate colored limestones are associated 



*The field work of 1889 was devoted so closely to the Pre-Paleozoic rocks that enough 

 time was not left for a complete examination of the later sediments. Although much evi- 

 dence has been collected bearing upon points here treated, just conclusions can not be drawn 

 in detail without more study with especial reference to the elucidation of doubtful points. 



