824 HISTORICAL GEOLOGY. 



In Tennessee and Kentucky, the Ripley group is represented chiefly by micaceous clays 

 and sand-beds ; and, while the thickness is 400' to 500' in Tennessee, it becomes a few 

 scores of feet in Kentucky. 



Below it, in southei'n Tennessee, lie 200' to 300' of beds, sparingly calcareous, repre- 

 senting the Rotten limestone, and at bottom, the "Coffee sands of Safford, 200' thick" ; 

 which are Lower Cretaceous. The age of the beds below the Ripley group on the Gulf 

 border, as Stanton remarks, is not clearly defined by the fossils, and the Colorado epoch 

 is therefore not known positively to be represented. The Rotten limestone contains many 

 Ripley fossils. During the Laramie epoch, according to White and Stanton, the Atlantic 

 and Gulf borders were probably somewhat emerged, the Ripley beds being covered directly 

 by beds with Eocene fossils. 



Weste7-n Gulf Border. 



In Texas, the Upper Cretaceous beds are 2000 feet tMck (R. T. Hill). 

 There are sand-beds and clays at base which are non-marine ; and above these 

 thick beds of limestone with much chalk, followed by marls and greensand. 

 They extend northeastward into Arkansas, and westward through the Trans- 

 Pecos region and its mountains, to northeastern Mexico, where they occur 

 in the states of Chihuahua, Coahuila, and Tamaulipas, chiefly along the 

 mountain region between Presidio del Norte and Tampico, resting on the 

 Lower Cretaceous conformably, although upturned. 



The subdivisions, as determined by Hill, are as follows : — 



4. Laramie Epoch. — 



Laramie series in western Texas. 



3. Montana Epoch. — 



Exogyra ponderosa marls, with glauconitic (or greensand) beds 

 (Navarro beds, Eagle Pass beds) above: chalk, overlaid by marls 

 and greensand. 



2. Colorado Epoch. — 



2. Austin limestone, or Austin-Dallas chalk ; 300 to 500 feet thick. 

 1. Eagle Ford shales; 500 feet thick. 



1. Dakota Epoch. — 



Lower Cross Timber sands; 300 feet thick. 



The beds are marine, excepting the sand and clays of the Lower Cross 

 Timber sands, and some beds of the Eagle Eord shales. The fossils are all 

 different from those of the Lower Cretaceous beds. The Glauconite group 

 contains over 40 species of fossils, identical, according to Stanton, with those 

 of the Ripley fauna, and many also of the species of the Montana group in 

 the Continental Interior. 



Continental Literior. 



The Cretaceous beds of the Interior Continental Sea were early studied 

 by Meek and Hayden, and their subdivisions in the main are those still 

 in use. 



