UPPER PALEOZOIC (CARBONIc). 255 
the Mississippi Basin. The western limit of the Lower Car- 
bonic must be concealed by a long overlap. 
Within the Plateau Province, the area drained by the Colo- 
rado river and deeply trenched by that stream and its tribi,itaries, 
the Carbonic column has been divided into 
Upper Aubrey. 
Lower Aubrey, 
Eed Wall. 
Lodore. 
The first two consist of sandstones with some limestone, but 
limestone predominates in the third, while the fourth is made up 
of sandstone and shale. The Upper Aubrey has been subdi- 
vided into 
Bellerophon Limestone. 
Yampa Sandstone. 
No fossils have been described from the Lodore, but the 
others yield abundant examples of Coal-Measures forms, many 
of these being identical with species occurring in the Mississippi 
Basin. 
In the region known as the Basin Ranges, including parts of 
Utah, Nevada and Arizona, Lower Carbonic forms occur at 
many places,. but are usually associated with Upper Carbonic 
forms. A distinctive Lower Carbonic fauna has been- recoo:- 
nized at a few limited localities in Utah, Nevada, Idaho and 
Montana ; but these localities are exceedingly circumscribed. 
The paleontologists agree in the statement that, except at the 
localities mentioned, the Carbonic rocks of the far Western 
mountain and plateau region exhibit a commingling of the inver- 
tebrate types which characterize the different divisions of the 
Carbonic as they are recognized in the Mississippi Valley; 
Within California the Carboniferous rocks are mostly shales, 
holding lenticular masses of limestone. The fossils thus far ob- 
tained hardly justify an attempt at detailed comparison with 
other areas. 
The subjoined table is offered to represent the grouping for the 
Appalachian region and the Mississippi Valley : 
