THE JURASSIC PERIOD. 63 



farther north. . The fossils of the early Jurassic beds point to fauna! 

 connections with central Europe. 1 



The Middle Jurassic of the Pacific coast, corresponding in a gen- 

 eral way with the Lower Oolitic of England, and the Middle Jura of 

 the continent of Europe, has a distribution similar to that of the Lower, 

 and its close association with the latter allies it closely with the Trias 

 stratigraphically. The auriferous slates of California, a meta-sedi- 

 mentary series, involve some Jurassic beds as well as those of greater 

 age (Trias, Carboniferous, and Silurian). 2 



Lower and Middle Jura in the western interior. — Between the 

 meridians of 106° and 112°, and the parallels of 35° and 42°, there 

 are beds of a sandy nature which have often been referred to the Ju- 

 rassic system. Their distribution is more restricted than that of the 

 Permian and Triassic Red Beds already referred to. The lower beds 

 which have been regarded as Jurassic are without fossils, and corre- 

 spond, in their general character, with the Permian and Triassic of 

 the same region. 



The beds of the western interior usually referred to the Permian, 

 Triassic and early Jurassic, have the appearance of a unit. Their 

 general (though not universal, see p. 26) conformity among them- 

 selves and with the Carboniferous below, seems to show that their 

 deposition followed the Carboniferous without notable interruption 

 in most places; but such evidence is to be received with caution, as 

 seeming conformities sometimes conceal great intervals. Since their 

 thickness is not great — 600 feet perhaps is an average — and since so 

 slight a thickness of coarse sediment does not seem to call for a long 

 period of time, there is some doubt whether any part of the Red Beds 

 is so young as Jurassic. The region of the Red Beds may have been 

 a land area, and subject to degradation during the early part of the 

 Jurassic period. In the later part of this period, as will be shown 

 later, the sea found access to the northern part of the Great Plains 

 area. If the Red Beds were suffering erosion during the earlier part 

 of the Jurassic period, and the region to the south throughout the 

 whole period, the thickness of the Permo-Triassic formations may 

 have been greatly reduced before the deposition of the Upper Jurassic 

 and Lower Cretaceous formations. In any case, the existence of 



1 Smith, J. P., Jour, of Geol., Vol. 111,1895, pp. 377-8. 

 'Idem., Bull. Geol. Soc. of Am., Vol. V, p. 257. 



