272 CENTRAL MINERAL REGION OF TEXAS. 



SECTION D. 



East of the Riley Mountains, south of Honey Creek, north of Sandy Creek, 

 and west of Packsaddle Mountain, there is a peculiar plateau in which a 

 very good section of the Fernandan rocks may be secured, owing to a rare 

 combination of favorable circumstances. Here the folds seem to have been 

 less pronounced, so that the dips are comparatively slight. The intrusive 

 masses have been less effective and the later upheavals have caused faults 

 around the edges of the area, so as to leave the field in a fair condition for 

 studying the events of the Fernandan Period. Moreover, the erosion here 

 has been of a character to expose the beds well. 



Below is given a general section across the strike (north 36 degrees west), 

 in a part of this area where the dip averages from 25 degrees to 40 degrees 

 south 54 degrees west, beginning above: 



1. Blue dolomitic marbles, coarsely crystalline, with bands of tougher, mottled, dark 

 marble. 



2. Tough, shaly slates and schists of chloritic aspect, variable. 



3. Blue graphitic and coal-black carbonaceous schists, more or less siliceous. 



4. Magnetite and hematite (altered) series, including magnetic schists. 



5. Sandy, fine-grained quartzites, shading into 



6. A well developed set of granular schistose and micaceous metamorphics, exhibiting 

 evidences of detrital origin. 



1. An uncertain set of hornblendic and other semibasic schists, whose texture and 

 structure do not indicate in all cases a positively aqueous origin. 



OTHER SECTIONS. 



By omitting from Sections A, B, and C such numbers as are not common 

 to all exposures — a good proof in our region that they are intrusive or extru- 

 sive — and by combining incomplete sections and those which are isolated, it 

 will readily be seen that section D is very comprehensive, including all the 

 members in the sequence as exhibited elsewhere. A. very large number of 

 disjointed sections might be given, fitted together by rejecting the overlaps, 

 and they would all confirm this as the typical section. There are many ex- 

 posures in which one or other of the seven lithologic sets appears to be ab- 

 sent upon cursory observation, but I have always found that close examina- 

 tion in such cases reveals as much of this type section as local circumstances 

 of erosion and subsequent deposition of detritus will demand as an assurance 

 of orignal completeness. 



THE GENERAL SECTION. 



From the foregoing examples it will be seen that with a general similarity 

 of lithologic composition, and with an induced general structure which has 

 brought all the Fernandan Beds into one strike, there are, nevertheless, two 



