6 iNTRODtrcTIOTf. 



along the route, and they indicate to us the Cretaceous age of the Llano 

 Estacado. 



" Further evidence of this is found in the collection made by Captain 

 John Pope on the Llano further south, near the parallel of 32. 



" He procured specimens of G-ryphsea in the bluffs of the Llano at the 

 Big Springs of the Colorado, and also on the surface, near the [southern 

 end of the] sandhills, and these fossils, together with the specimens of the 

 strata and other evidences, led me to describe the Llano as Cretaceous, in 

 the report on the geology of that route. 



' ' The Llano is doubtless continuous southeasterly from these localities 

 to vicinity of Austin and San Antonio, where it forms bluffs filled with 

 Cretaceous fossils, already described by Ferdinand Eoemer. 



' ' There is thus little doubt the strata of the Llano Estacado and the 

 other plateaux along the route, resting upon the gypsum formation, are 

 of Cretaceous ag^, surmounted, perhaps, in places by more recent de- 

 posits."* 



These Cretaceous fossils were the evidence which carried most weight 

 with him, although, as we have seen, before he recognized the litho- 

 logical resemblance of the Llano materials to those of Tertiary age. 



He continues: " There is much reason to believe that the Cretaceous 

 strata of the Llano are surmounted by Tertiary deposits over a part of 

 the Plain. This is indicated by the second line of bluffs, or second step, 

 seen from the valley of the Canadian. Dr. Shumard also, who examined 

 the Llano at the sources of the Red River, found a layer of rounded 

 gravel and pebbles upon the top, which he denominates drift, and which 

 at some places was found to be about 100 feet thick. Fragments of agate 

 and carnelian, and of silicified wood, appear to abound in this deposit. 

 The same pebbly bed appears to be found west of the Sierra Madre, on 

 the table lands of Zuni and its vicinity. These are in all probability 

 Tertiary or Post-Tertiary deposits; but as they are not characterized by 

 fossils, and as their extent is not known, I have not indicated them on 

 the map." 



These are the first references of these beds to a Cenozoic age, and they 

 are based upon as good evidence as any that is adduced in any subsequent 

 publication prior to those of this Survey. 



On the geological map prepared by Profs. Hall and Lesley to ac- 

 company the report of Major W. H. Emory on the United States and 

 Mexican Boundary Survey, t a portion of the Llano Estacado is colored 



*Pages 79, 80. 



t Washington, 1857. 



