504 THE JURASSIC PERIOD 



those of the Queen Charlotte Islands and British Columbia, as to 

 suggest that the waters entered from the northwest (Fig. 423). 

 The presence in some parts of the western interior, of fjesh-water 

 beds (Morrison beds of Colorado, Montana, and Wyoming) regarded 

 by some as of late Jurassic age, would, were their age established, 



Fig. 425. Lower part of the LaPlata (Jurassic) sandstone, southwest of La Sal 

 Mountains, Utah. (Cross, U. S. Geol. Surv.) 



show that the sea-water withdrew before the end of the period. If 

 not Jurassic, the beds in question are Comanchean. 



Marine Jurassic limestone occurs in western Texas. Its con- 

 nections are probably southward with the Jurassic of Mexico, where 

 the system is well developed. 



Pacific coast. Marine deposition was in progress on the Pacific 

 coast, though much of the system here is concealed beneath younger 

 formations. In the latitude of Nevada and Utah, the earlier 



Fig. 426. A section in southern Montana. JR = Archean; ^, Cambrian; 

 Devonian; Mm, Mississippian; Pq, Pennsylvanian; Je, Jurassic; Kd, Kmc, and 

 Kl, Cretaceous; bbr, igneous rock. (Peale, U. S. Geol. Surv.) 



formations of the period extended east to longitude 117. The 

 Lower Jurassic beds generally rest on the Trias conformably where 



