THE CARBONIFEROUS SYSTEM. 91 
seventy to seventy-five feet of argillaceous shale, of which the upper por- 
tion is generally of a marked red color, while the lower portion is dark 
bluish gray. These shales are very variable in their relative thickness, 
sometimes one or the other filling the entire interval between the Berea 
grit above and the black Cleveland shale below, sometimes that interval 
being equally divided between them, and sometimes again one or the 
other greatly preponderating, while both are present. In the section 
exposed at Bedford the red shale is scarcely visible, while it is met with 
at Newburgh, five miles distant, and in the hills east of Cleveland fills 
the larger part of the interval that separates the Berea grit from the 
black shale which underlies the East Cleveland quarries. At Berea and 
Elyria both shales are visible, while on the Vermilion—which takes its 
name from this circumstance—the red shale is much more largely devel- 
oped, and attains a thickness of something like sixty feet. In most 
localities where the Bedford shale is exposed, the upper surface is very 
irregular, and it is evident that this formation has been extensively 
eroded by the agency which transported the beds of sand now consoli- 
dated into the Berea erit. It is probably due to this fact that the red 
shale is so frequently found to be wanting in the section. In the red 
shale no fossils have as yet been discovered, doubtless for the same rea- 
son that fossils are so generally absent from the sediments that contain 
a sufficient amount of peroxide of iron to derive their color from this 
source. The explanation of this phenomenon is very simple. The action 
of carbon upon the sesquioxide of iron is to reduce it to the protoxide by 
the absorption of one equivalent of its oxygen, so that in all deposits which 
contain, when accumulating, a considerable percentage of organic matter, 
this serves to reduce the iron to the protoxide, which imparts a bluish 
or greenish color to the deposit. Where organic matter is absent the 
iron passes to the condition of peroxide, and in this state, though in 
small quantity, it communicates a bright red color to the materials im- 
pregnated by it. 
The lower portion of the Bedford shale, though, like the upper part, 
very fine and argillaceous, is generally dark gray or blue in color, con- 
tains considerable lime, and is locally highly fossiliferous. The fossils 
are most abundant in that portion which rests immediately upon the 
black shale below, and here they are sometimes so numerous as to form 
a large part of the mass. 
The following are some of the fossils derived from this horizon: Syrin- 
gothyris typa, Win.; Orthis Michelini, Lev.; Spiriferina solidirostris, White ; 
Macrodon Hamiltonix, Hall; Hemipronites crenistria, Phil.; Chonetes Logant, 
Hall; Lingula Cuyahoga, Hall ; Rhynchonella Sagerana, Win. 
