iNTRODUCTIOIir. 5 



Indeed, all the specimens of the sandstones of the Llano are so much like 

 those of the Tertiary, tliat if it were not for the presence of Cretaceous 

 fossils, I would have been led to regard them as of that period." 



Again he says (p. 21): 



" The drift deposit, which has been described by Dr. Shumard as cover- 

 ing the rocks of the Llano, may, and very probably does, belong to the age 

 of the Tertiary; but the materials and facts that were procured by Cap- 

 tain Pope are not sufficient to warrant any conclusions on this point." 



In his description of the building stones of the collection, he says of 

 those from the Llano Estacado: 



"All these specimens have a modern look and resemble the Tertiary 

 sandstones along the margin of the Colorado desert, where some of the 

 upper beds are highly charged with carbonate of lime in the form of trav- 

 ertine, or calcareous tufa." 



The survey along the thirty-fifth parallel had with them as geologist 

 Mr. Jules Marcou. In his field notes, published in Volume III of the 

 same report, he gives the following section, which he says " is the same at 

 the foot of the Llano:" 



" "White limestone. 



" Calcareous conglomerate. 



"Limestone. 



' ' Sandstone with numerous calcareous concretions. 



' ' Red sandy marls of the New Red. ' ' 



According to the journal here published, Mr. Marcou at first regarded 

 the plains as probably Cretaceous, but afterwards decided that they were 

 Jurassic. 



In his Geology of North America* lie very fully gives his reasons for 

 assigning it to this period, which are, the finding of fossils that he con- 

 sidered identical with European forms belonging to the Jurassic, in Pyr- 

 amid mountain, which he considers as a continuation of the deposits of 

 the Llano. He, therefore, colors the Llano as Jurassic in the map accom- 

 panying his work. 



Mr. Blake, who discusses the geology of this line also, differs from Mr. 

 Marcou, and from his understanding of the paleontological evidence 

 makes the Plains Cretaceous. He states as follows (p. 80) : 



" Most, if not all, of these Cretaceous fossils were procured from the 

 edges of the horizontal strata which compose the extensive table-lands 



♦Zurich, 1858. 



