108 GEOLOGY. 



drawn chiefly from the phenomena of the old world, concludes that 

 if the distinctness of the Lower and Upper Cretaceous had been known 

 when the accepted time-divisions were established, they would have 

 been made separate divisions of equal rank with the Triassic, Jurassic, 

 etc. The Lower and Upper Cretaceous are therefore here considered 

 as two somewhat closely associated periods, coordinate with the Triassic 

 and Jurassic. 



The following table (p. 109) gives some idea of the relations of the 

 two systems, and of their parts, though the correlations for different 

 regions are not to be regarded as exact. 



The Comanchean (Shastan, Lower Cretaceous) System. 1 



The warping which marked the opening of the Comanchean period 

 occasioned the development of extensive lakes or other basins of 

 non-marine deposition in some parts of the continent, while other 

 parts were depressed beneath the sea. The Comanchean deposits of 

 the Atlantic and Eastern-Gulf . coastal plains, and in certain parts of 

 the western interior, are non-marine; those of the western Gulf region, 

 extending as far north as the Ouachita Mountains and even a little 

 beyond, are chiefly marine, while those of the Pacific coast are wholly 

 so. From the distribution of the marine strata of the system, it is 

 clear that by far the larger part of the continent was above sea level 

 during the period, unless the deposits have been extensively removed 

 by erosion, and this does not appear to be the case. 



The Atlantic and Gulf Border Regions. 



To understand the relations of the Cretaceous on the Atlantic 

 coast, 2 it should be recalled that during most of the Paleozoic era, 

 the area east of the Appalachians, as far as the present coast and 

 beyond, was land, and that when the Appalachians came into exist- 

 ence at the close of the Paleozoic, some parts of Appalachia were bowed 

 or broken so as to become the sites of deposition, and here the Triassic 



1 For an excellent summary of the Lower Cretaceous, see Stanton's Lower Cre- 

 taceous Formations and Faunas, Jour, of Geol., Vol. V, 1897, pp. .579-010. As the 

 title implies, this paper deals with paleontological, rather than physical questions 

 Full bibliography. 



2 Data concerning the Lower Cretaceous formations of the Atlantic coast are to 

 be found in reports of the Geological Surveys of Xew Jersey and Maryland (Vol. I). 

 See also McGee, article cited below. 



