Marcous Geological Map of the United States. 387 



Wislizenus and others along the valley of the Canadian river 

 not far from Pyramid Mount, where the Gryphcea was procured. 

 Farther east on the False Washita and near the Canadian, the 

 Cretaceous fossil Gryphcea Pitcheri occurs in abundance and near 

 the great beds of gypsum. Leon Spring, in the southern part of 

 the Llano, has afforded abundance of Cretaceous fossils, and this 

 place is represented on the map as Jurassic. Cretaceous fossils 

 were also obtained by Capt. Pope from the bluffs of the Llano 

 at the Sulphur Springs of the Colorado and from the surface of 

 the plateau near the Sand Hills.* The Llano of Texas is well 

 known and is undoubtedly the continuation of the Llano Esta- 

 cado. The bluffs are filled with Cretaceous fossils already de- 

 scribed by Ferdinand Kcemer. They are correctly represented 

 as Cretaceous on the map. 



The map displays a most remarkable relation of position be- 

 tween the Cretaceous and the " Jurassic" along the valley of the 

 Eio Grrande between El Paso and the mouth of the Pecos. The 

 river has cut its valley downwards through the horizontal forma- 

 tions of the Llano which form bluffs on each side. On the map 

 we find the valley of the stream colored as Cretaceous, while the 

 higher strata of the Llano, are colored as Jurassic. Thus, according 

 to this representation, the Jurassic strata overlie the Cretaceous. 

 This conclusion is unavoidable unless we are ready to believe 

 that the Cretaceous strata were deposited since the erosion of the 

 valley of the Eio Grande. The same alternative is presented to 

 us along the Upper Missouri ; the highest table-land is colored as 

 Jurassic, and the Cretaceous is made to crop out lower down 

 nearer the river and rests directly upon the formation called Trias. 



But the most striking feature of the map remains to be no- 

 ticed. "We find an area equal to that of all the States east of the 

 Mississippi colored as Triassic. The section also represents this 

 formation as enormously thick, and with four divisions corres- 

 ponding to those in Europe. The color is extended on the map 

 along the whole course of the Missouri down to Council Bluffs ; 

 and south into Texas, and is carried east so as to reach and bor- 

 der the southern shore of Lake Superior. The basis of this repre- 

 sentation is chiefly the occurrence of red gypseous strata along 

 the False Washita and Canadian rivers. The upper limit of the 

 formation is considered to be at the base of the so-called Juras- 

 sic strata of the Llano, and its lower upon the Carboniferous. 



The representation of this broad area as Triassic is made with- 

 out the evidence of a single characteristic fossil, the principal 

 support for it being the position and mineral characters of the 

 strata. It is said that they are like those of Windsor and Plaister 

 Cove, N. S., which were supposed to be Triassic but have since 

 been shown by Mr. Dawson to be Carboniferous.f Hence the 



* Report on the Geology of the Route surveyed by Bvt. Capt. Pope, U. S. Top- 

 Engrs., 4to. Washington, 1856. [Pacific R. R. Exp. and Surveys.] 

 f Acadian Geology < by J; W. Dawson. Edinburgh; 185&. 



