FORMER CONTINUITY* OF THE CRETACEOUS STRATA. 527 



Texas state survey takes the ground that this Paleozoic area was an island 

 in the Cretaceous sea, it is interesting to see how far the facts aqcord with 

 this theory. From the statements communicated by Professor Hill and 

 from analogy it seems that he must be correct, and that the Cretaceous over- 

 lapped this central area ; otherwise it would now be reduced to base-level by 

 erosion. I should like to hear what the geologists of the Texas state survey 

 who are present have to say about this theory. 



Mr. E. T. DuMBLE : I am not personally acquainted with the geology of 

 the central area save in a general way. Dr. Comstock, who is in charge of 

 the district, has given in his report some of the reasons why he considers this 

 area to never have been covered with the Cretaceous rocks ; among other 

 reasons, urging that many points of this area are higher than any points of 

 the surrounding Cretaceous area. 



Professor Hill : Generally one can look over the Paleozoic area from the 

 Cretaceous escarpment. It may be true that the Paleozoic does, in some 

 places, rise to the level of the Cretaceous escarpment ; but it is necessary to 

 have at least 4,000 feet of Cretaceous strata removed to bring the two 

 horizons on a level, and consequently the Paleozoic would require to be at 

 least that much higher than the present escarpment to have been uncovered 

 by the Cretaceous sea. 



Dr. Cooper Curtice: To what has already been said in regard to the 

 erosion of the escarpment surrounding the central basin of Texas, I wish to 

 contribute the following remarks : 



In going from Burnet, Texas, situated on the edge of the escarpment, 

 southward to Marble falls, on the Colorado river, one successively crosses the 

 following strata : lower Cretaceous, Burnet marble series (either Carbonifer- 

 ous or Silurian), Potsdam, Capitol granites, and Carboniferous. The Burnet 

 marble appears to abut against the Potsdam sandstone. The sandstones rest 

 horizontally upon the granites, and their lower beds are made of small 

 masses of feldspar and quartz entirely like that of the granite. The sum- 

 mits of the sandstone beds rise over a hundred feet higher than the Car- 

 boniferous at Shinbone ridge, which thSy approach to within a couple 

 of miles. 



The semi-crystalline limestones of Shinbone ridge abut against the granites, 

 but dip away from them. Carboniferous fossils were found within a very 

 short distance from the contact, in an abandoned prospect hole. These lime- 

 stones were on a level with the granites, or about on a level with the base of 

 the Potsdam sandstone. 



On the road westward from Burnet to Bluffton the following exposures 

 were observed : Near Spring creek, a contact of the Burnet marble with 

 Potsdam (Lmgula-hesir'mg) sandstones, with the Potsdam lying on granites ; 

 between Spring creek and Clear creek, apparently stratified granites ; at 



LXXVII— BuiJ,. Geoi,. Soc. Am , Vol. 2, IS'.U). 



