MESOZOIC TIME — CRETACEOUS. 



815 



Atlantic and Continental Interior being almost completely unlike, it has 

 proved very difficult to determine equivalency. 



The Lower Cretaceous series is less well displayed on the Atlantic and 

 Pacific borders than in Texas, and hence the division into epochs has been based 

 on the subdivisions recognized in the latter region. For a like reason the 

 epochs of the Upper Cretaceous are based on the subdivisions over the Con- 

 tinental Interior. 



The principal subdivisions in each of the geographical belts are given in 

 the following tables. The equivalency indicated is, for the reasons stated, 

 largely doubtful. For comparison, the corresponding subdivisions in Euro- 

 pean geology are presented in the last column. 



1. Lower Cretaceous Division. 



Atlantic and 



Northern Gulf 



Borders 



Western Gulf Bor- 

 der, Texas 



Rocky Mountain 

 Region 



Pacific Border 



Europe 



1, 2, 8, 

 group, 



Potomac 



Atlantic 

 border ; Tusca- 

 loosa group, Ala.; 

 Eutaw in Miss. 



'8. Washita 



Epoch 

 2. Fkedericks- 



BURG Epoch 

 1. Trinity 



Epoch 



1. Kootanie Group 



Horsetown 



Knoxville 



8. Gault or Albian 

 2. Aptian or Lower 

 Greensand 



>1. Neocomian 



2. Upper Cretaceous Division. 



Atlantic 

 Border 



Northern Gulf 

 Border 



Western Gulf 

 Border, Tezas 



Continental Interior 



and Rocky Mountain 



Region 



Pacific Border 



Europe 





Unrepre- 

 sented ? 

 Upper 

 Greensand 

 - in part. 







4. Laramie Epoch 





Dan IAN 



4.- 



Unrepresented? 



Laramie in 

 western 

 Texas 



2. Upper Laramie 

 or 

 Denver group 

 1. Lower Laramie 





Maestricht 

 beds 



f Middle 



Greensand 



Lower 

 [Greensand 



2. Clay marls? 



Eipley group ; 

 part of Eotten 

 limestone 



Lower part of 

 Eotten lime- 



f2. Glauconitic 



group 



1. Ponderosa 



marls 



'2. Austin 



3. Montana Epoch 

 2. Fox Hills group 

 1. Fort Pierre group 



2. Colorado Epoch 



Chico group, 

 or upper 

 . part of the 



Senonian 

 Ttjeonian 





stone. Upper 



limestone 



2. Niobrara group 



Shasta- 







Eutaw beds ; 



1. Eagle Ford 



1. Benton group 



Chico series 







Tombigbee 



shales 









1. Earitan 



sands 



Lower Cross- 



1. Dakota Epoch 





Cbnomanian 



group 





Timber sands 



Dakota group 







The lower limit of the Cretaceous series in Korth America has been 

 made out by a comparison of fossils with those of the Neocomian of Europe. 

 It is especially marked, in most localities where the remains of plants occur, 

 by the presence of the leaves of the earliest species of Angiosperms, along 

 with those of the still abundant Cycads. As at present understood, the 



