658 CENTRAL MINERAL REGION OF TEXAS. 



counties. As will be seen from the sections (Figs. 1 to 9), the complications 

 in structure are too great to make the study a simple one in all cases, and 

 thus it may be difficult to connect isolated patches with each other by contin- 

 uous sections in many tracts. Still, familiarity with all the exposures enables 

 one to work out structure which can not be understood except by careful 

 mapping, topographic as well as geologic. This has been done by myself, 

 and my conclusions are based upon a complete knowledge of the field. 



Thirdly. The basal members of the Fernandian System are made up in 

 part of material apparently derived from the Burnetian rocks. 



Fourthly. There are geologic foci where two or more of the orographic 

 axes cross, and often in such places the chronologic relations of the Archean 

 systems are distinctly and unmistakably recorded. On Little Llano Creek, 

 south of Lone Grove, Llano County, and in the region of the Dragon Fangs, 

 on Honey Creek, Mason County, there are very good examples, but many 

 more might be given. I have seen the same evidence beautifully recorded 

 in the Wichita Mountains, in Indian Territory. In situations like these the 

 Burnetian gneisses have often been turned from their normal trend and 

 curved into the northwest trend of the Fernandian axis in such manner as 

 to leave no doubt of the proper relations of the two systems. 



Fifthly. The completed Geologic Map and the actual sections made with 

 great care afford the most convincing testimony (in my judgment) that my 

 conclusions are in accordance with the facts.* 



EPARCHEAN ROCKS. 



THE TEXLAN (ALGONKIAN?) SYSTEM. 



The relations of the Texian strata to the Fernandian are deduced from 

 facts of the same character as those used to determine the taxonomy of the 

 Archean systems. 



First. The nearly due north- south strike in which these beds are com- 

 monly (not always) lying is peculiar to them ; the earlier fractures and lines 



*In 1889, preparatory to making plans for the survey of this district, I devoted sixteen 

 days to its cursory examination. The general idea thus gained of its geology was as foreign 

 to the results of two years' detailed study as could well be. Several tons of specimens were 

 collected the first year and many boxes the second field season. The topography and geol- 

 ogy have been mapped minutely, and the field notes of myself and assistants cover some 

 three thousand pages, in thirty-eight note books. These have been plotted and studied for 

 twenty-four months, without bias of any kind. Eor these reasons, while some may feel 

 called upon to differ from my opinions, after a run of a day or two across a portion of the 

 district or without seeing the region, I am fully satisfied that upon more detailed investiga- 

 tion my conclusions will be upheld. 



