308 CENTRAL MINERAL REGION OF TEXAS. 



other follows the same course along the valley of another Honey Creek in 

 Mason County, six miles west of Mason City. The former locality is the one 

 observed, in part, by Mr. Walcott, and the one which forms the foundation 

 for his mistaken reference of all the Central Texas granites to a Pre-Potsdam 

 age.* In both these outcrops there are coarsely crystalline granites entomb- 

 ing masses of schists of a character similar to the adjacent country rock. 

 Mr. "Walcott was the first to report this fact, but he failed to observe the true 

 relations of this granite to the other strata, its wholly different character from 

 all other granites of the region, and the series of fractures in Packsaddle 

 Mountain corresponding to the trend of this granite eruption. 



It is remarkable that these particular masses are the only examples of 

 schist enclosures in the granite of our region. The granite itself is often 

 nearly white or dull grey, and the black schists form nuggets, or pockets, 

 distributed irregularly through the base, but invariably in intimate associa- 

 tion, and usually welded into the matrix, if not materially altered at the 

 edges. Often both the schist and the granite are mutually blended into one 

 another at the contact, and the original schist structure is very rarely retained, 

 except in very thick masses. In the smaller inclusions re-crystalization has 

 frequently taken place to such an extent as to leave no evidence of the pre- 

 vious condition, and sometimes the reaction of the enclosed schist upon the 

 granite has been strong enough to alter the mineral composition of the latter 

 in its neighborhood. Occasionally, where there are good exposures of the 

 adjacent schists in the same trend, slips have occurred, leaving wedges of 

 comminuted schists and granite with "slickensides." Over wide tracts the 

 hard granite is covered with a thoroughly decomposed granite 10 to 30 feet 

 thick. There seems good warrant for the belief that the present exposures 

 are due to denudation of superincumbent strata, but it is almost impossible 

 now to determine whether the Silurian system was represented here by any 

 members at the time of the uplift, although there are some facts which seem 

 to make this improbable. Taking into account the extent and character of 

 the breaks, and the structure, texture, and composition of the granite, I am 

 inclined to believe that this Post-Silurian outburst was of the nature of a 

 sudden release of long continued tension along a line which had not exhibited 

 weakness prior to that time. This view is greatly strengthened by the fact 

 that the same trend has a different aspect, more like the earlier uplifts, in 

 places where an intermediate environment exists; thus for instance, a little 

 west of Cold Creek, and elsewhere, the Texan and later strata have been 

 violently thrown into the breaches caused by this irruption. In other cases, 

 where the capping has certainly extended to the Cambrian strata, these have 



* Op. cit. American Journal of Science, vol. XXVIII, 1884, p. 431. 



