362 CHARLES S. PROSSER 
how, as the Chagrin formation is followed westward from Rocky 
River along the lake shore and in the stream valleys, that thin layers 
of black shale appear in the typical blue and gray shales of the 
Chagrin. These alternating layers of blue and black shales were 
found in the lower courses of the Black and Vermilion rivers, while 
on the Huron River, the typical locality of the Huron shale, it 
was seen that this formation consists of a certain number of zones 
of practically pure black shale alternating with those that are com- 
posed of generally rather thin zones of blue to gray shale alternating 
with black shale. The formation has a thickness of over 200 ft. in 
the Huron River region and the thick zones of black shale contain 
spherical concretions of variable size. The invertebrate, verte- 
brate, and plant fossils contained in the Huron shale are of Devonian 
age according to the opinions of at least most paleontologists who 
have recently studied them.t The Cleveland, composed mainly of 
black, bituminous shale containing lens-shaped layers with cone-in- 
cone structure and without spherical concretions, overlies the 
Chagrin formation in the Cleveland region and on Rocky River, 
while to the west in other streams or in the cliffs of the lake shore 
nearly, if not quite, as far as Lake Breeze it overlies the alternating 
blue to gray and black shales with thin sandstones. The Cleve- 
land shale overlies similar alternating shales in the Black and 
Vermilion river valleys and the Huron shale in the Norwalk region. 
The thickness of the Bedford formation is variable in all this region, 
largely due to the erosion of its upper surface before the deposition 
of the Berea sandstone, which was perhaps in general greatest in 
the Norwalk region where frequently all of the formation is wanting 
and at most only the lower part remains. The Bedford fauna and 
the disconformity between the Bedford or Ohio shale and Berea 
formations favors drawing the line of separation between the 
Devonian and Mississippian at this horizon. It appears clear that 
the upper black shale crossing this district is the Cleveland, that 
the Huron shale in general is the western lithologically more or 
less changed stratigraphic equivalent of the Chagrin formation, 
and that both the stratigraphic and paleontologic evidence agree 
in referring it to the Devonian. 
‘For a summary of these opinions see Geological Survey of Ohio, Bulletin 15, 
chap. vi, 509-29. 
