INTRODUCTION. 251 



Central region to justify them in thus adjusting it. But their generalizations 

 were undoubtedly the best that could be made without further investigation 

 than they were able to undertake, and some of the conclusions of Mr. Hill, 

 especially, are remarkably able, considering the limits of his field of observa- 

 tion. The assignment of the basal rocks at Burnet to the Carboniferous is 

 untenable. Shumard referred them to the Calciferous epoch as early as 

 1859;* and the present writer has traced them continuously from the un- 

 doubted Silurian outcrops farther west and south. But the real facts could 

 hardly fail to escape one passing rapidly across the country. 



In the American Geologist for January and February, 1890, Mr. Hill 

 has also two very valuable papers which incidentally touch upon the geologic 

 history of the Central Paleozoic area.f He says (p. 24): 



The detailed stratigraphy and structure of these important regions are unrecorded in geo- 

 logic literature. But it is evident from the few cursory examinations I have been able to 

 give it, that it is what was once a region of much disturbance, but not so excessive as the 

 folding of the Ouachitas or Appalachians. While the latter have remained above oceanic 

 inundation since Carboniferous time, their Texas counterparts were buried probably beneath 

 thousands of feet of sediments during the Lower and Upper Cretaceous subsidences. * * 

 That thev are at present exposed through the erosion of the thousands of feet of Cretaceous 

 sediments that once covered them is evident. 



The only other paper prior to 1890 that touches even remotely upon the 

 geology of the Central area is a very brief outline given by Mr. W. E. Hid- 

 den, in connection with a description of the Barringer tract, in Llano County, 

 from which rare minerals have recently been obtained. J 



This writer remarks that ''the whole surrounding region for many miles is 

 Archaean (with occasional cappings of limestone) and granite, in various 

 shades of color and texture, is the common country rock." Mr. Hidden 

 quotes Hill for this Archaean designation, but unfortunately he has not veri- 

 fied his reference, for there is no place in any of Mr. Hill's writings where, 

 upon his own responsibility, he has classed this or any other portion of the 

 Central area as Archaean, while in the paper quoted by Mr. Hidden there is 

 no mention whatever of the name Archaean. § 



* Trans. Acad. Sci., St. Louis, vol. I, No. 4, 1860, p. 672. 



f Classification and Origin of the Chief Geographic Features of the Texas Region. (Map.) 

 Robt. T. Hill. Amer. Geologist, vol. VII, pp. 9-29; II, pp. 68-80. 



X A description of several Yttria and Thoria minerals from Llano County, Texas. By W. B. 

 Hidden and Jacob B. Mackintosh. Amer. Jour. Sci., 3rd ser., vol. XXXVIII, Dec, 1889, pp. 

 474-486. Mr. Hidden is alone responsible for the description of the locality (pp. 474, 475) 

 from which the quotation is taken here, as Mr. Mackintosh never visited the spot. 



§A paper by Dr. Genth, published in Amer. Jour. Sci., 3rd ser., vol. XXXVIIL, Sept., 

 1889, pp. 198-9, describes the gadolinite of this locality (wrongly assigned to Burnet County), 

 but no geologic data are reported. 



