60 GEOLOGY. 



their distribution, and their stratigraphic relations are much more 

 closely allied to the Lower Cretaceous than to the Triassic. They 

 constitute the beginning of the great series of undeformed beds under- 

 lying the Coastal Plain. 



If deposits were not making within the present area of the land 

 along the Atlantic coast during the Jurassic period, geological processes 

 of another sort must have been there in operation. As already noted, 

 the Triassic period seems to have been closed by the deformation of 

 the Triassic beds, accompanied by faulting and the injection of lava 

 into the faulted series. Since the uplifted and deformed Triassic sys- 

 tem, along with the Appalachian Mountain region, was essentially 

 base-leveled before the Cretaceous period was far advanced, the inter- 

 vening Jurassic period must have been a time of great erosion, so far 

 as the Appalachian belt and the Piedmont plateau to the east were 

 concerned. The sediments worn from these older beds were of course 

 deposited somewhere, and the site of deposition seems to have been 

 chiefly east of the present coast. 



Aside from the doubtful beds referred to above, no Jurassic strata 

 are known on the eastern side of the continent. Marine Jurassic beds 

 have been recently reported from Texas, 1 but they lie to the west of 

 the ranges corresponding to the Rockies. These Jurassic beds are 

 limestone, and though the exposures are limited, their connections 

 are probably southward with the Jurassic of Mexico. In eastern Mexico, 2 

 Jurassic beds of marine origin are somewhat widespread, the later 

 formations of the period being more extensive than the earlier. The 

 Jurassic system is also said to be represented in the western part of 

 Cuba. 3 



The broad interior of the continent, including most or all of the 

 area which emerged during the closing stages of the Paleozoic, appears 

 to have remained above the sea during the Jurassic period, as during 

 the Triassic. The area of sedimentation was even more limited than 

 during the Triassic period, especially at the east, though later in the 

 period marine sedimentation was more widespread in the west than 



1 Cragin, Discovery of Marine Jurassic Rocks in Southwestern Texas. Jour, of 

 Geol., Vol. V. See also Hill, Am. Jour. Sci., Vol. II, 1897, p. 449, and Physical Geog- 

 raphy of Texas, Topographic Atlas, U. S. G. S. 



2 Bol. del. Inst. Geol. de Mexico, Nos. 4, 5 y 6, 1897, and Bain, Jour, of Geol., Vol. V, 

 p. 384. 



5 Hill, Cuba and Porto Rico. 



