VALLEY REGION ; CHARACTERS OF THE ROCKS. 158 
& group, are those of the Trenton limestone of New York. 
In places, particularly in the region south of the Cahaba 
Field in Bibb county, the uppermost beds of this formation, 
above the purer limestone mentioned, are calcareous shales 
and shaly limestones, often full of the fossil forms known as 
graptolites. Where these thin-bedded shaly limestones oc- 
cur abundantly forming the surface, cedar glades are quite 
characteristic. 
The valley between the Cahaba and the Coosa Coal 
Fields shows a wide belt of Trenton limestone, which 
is particularly pure and well developed near Pelham and 
Siluria in Shelby county, and southwards. Near Pratt’s 
Ferry on the Cuhaba, and stretching thence northeastward 
there is another great belt of it, containing some fine mar- 
bles, which have in a small degree been worked at Pratt’s 
Ferry. 
For the sake of completeness, I might add that the phase 
of the Silurian formation to which Prof. Safford in Ten- 
nessee has applied the name of Nashville, has its represen- 
tative in Alabama though not within the area shown on this 
map. 
The Clinton or Red Mountain Formation. —This is the third 
and uppermost of the divisions of the Silurian which we 
make in this State. The mass of the rocks of the Red 
Mountain are sandstones and shales, which show a great 
variety of color, yellow, red, brown, chocolate, and olive 
green, in this respect resembling the Montevallo Shales. 
Along with these are some calcareous and ferruginous rocks, 
the latter passing into beds of red iron ore, made up of 
small flattened nodules, shell casts, etc., of ferric oxide. 
In many places, where mining has penetrated the ore 
bed beyond the reach of atmospheric agencies, the ore 
is seen to be quite calcareous; in fact, a kind of highly 
ferruginous limestone, which, when used in the furnace, 
often contains lime enough to flux the ore. At the out- 
crop the ore is seldom calcareous, though often sandy. 
So far as I know there has been no very satisfactory expla- 
nation of the mode of formation of this ore. It is of very 
variable thickness up to twenty feet, and is in more than one 
bed. Itis a remarkable fact that while near Oxmoor the 
