Devonian Era in the Ohio Basin. — Claypole. 97 
The consideration of this question would not be complete 
without regarding another element in the problem. Much ma- 
terial has been collected since the monograph appeared. Could 
its author have seen the magnificent display of elasmobranch 
fossils which have been brought to light by Dr. Clark, the 
strongly Carboniferous aspect of such a fauna would have en- 
titled him to insist the more firmly on the allocation of the 
Cleveland shale on the higher horizon. With the exception 
of a few isolated teeth, no cladodonts were recognized from 
the Devonian in either hemisphere until a short time before 
Dr. Newberry's classic work appeared and only one or two in- 
distinct figures were there represented. The class in aspect 
was regarded as essentially Carboniferous or later. 
It does not necessarily follow that such allocation would 
have been unassailable. It may be quite as accordant with 
fact and with nature to carry the cladodonts back into Devonia 
as to move the great placoderms up into the Carboniferous.. 
Indeed, it would be a greater incongruity to see the latter, in- 
cluding of course, the venerable Coccosteus. swimming in the 
Carboniferous sea than to recognize the cladodont sharks as 
denizens of the waters of Devonia. 
Though only a few relics of the group were previously 
known, yet the presence of these few was sufficient proof of the 
existence of the family in pre-Carboniferous days; and when, 
further, we recollect that they even antedate the Devonian era 
itself and have left their remains in the strata of Siluria with 
those of the antique pteraspidians, we are forced to admit that 
the elasmobranch type is among the oldest vertebrate patterns 
that nature introduced, and may well be carried back into 
Devonia. 
Accordingly I prefer to retain the Cleveland shale as the 
conclusion of the lower system, regarding it at the same time 
as a departure from the type toward that of the next overlying, 
or Carboniferous. This decision is. of course, provisional. The 
discovery of fossils in the liedford shale may some day justify 
a reconsideration of the judgment . 
In the field, in many parts of the basin, this palseontological 
summit of the Devonian system is not easily discovered or, in- 
deed discoverable, and the working geologist will therefore he 
in practical difficulty. Rut the same is true on other' proposed 
