;',.") I The, American Geologist. June, 1896 
The interpretation is, therefore, that during the continued 
depression, which allowed the accumulation of the thick bar- 
ren shale iii Ohio and Pennsylvania, the Black Shale region 
was one of comparative stability wliere the succession of life 
went on unbroken but not unchanged. Consequently the time 
interval represented by the massive strata between the Cor- 
niferous and the Carboniferous of the east, sometimes reach- 
ing 15.000 feet, is not longer than that which is represented 
in central Ohio by the 300 or 400 feet that occupy the same 
taxonomic position in the geological column. Sedimentation 
in the former case must have proceeded very much more rap- 
idly than in the latter. 
Descending again we find the lower shale and its fish fossils 
underlain by the Corniferous, etc. limestone. This which forms 
the Devonian floor of the eastern half of the state is about 80 
feet thick and also contains fossil placoderms. But we have 
in our downward progress now lost our clue. Among the 
placoderms is no Dinichthys or any genus already seen. They 
consist of the following: 
Acantholepis pustulosa? Bhynchodus secans 
Acanthaspis armata " frangens 
Macropetalichthys sullivanti " crassus 
Asterosteus stenocephalias Dinichthys ? prcecursor 
< 'ocebsteus occidentalis 
It is true that the name Dinichthys appears in the above 
list, but its generic identification is very doubtful and no re- 
liance can be placed upon it for the purposes of argument. 
We encounter then at the top of this limestone a complete pal- 
eontological ichthyic break. No species and no genus crosses 
the line. Obviously the ancestor of Dinichthys must besought 
elsewhere. Macropetalichthys was, so far as can be deter- 
mined, a toothless species and very far from what a probable 
progenitor of Dinichthys might be expected to be. while Ony- 
chodus, though toothful enough, is built on a type totally 
different from that of the great Upper Devonian placoderms. 
Reflecting for a moment on the conditions of the era. into 
which space will not allow us here to enter, we find that the 
probable cause of the change in the Ohio area at the end of 
the Corniferous period was due to the uplift of a great region 
in the northeast whose wash was sent down into the Appala- 
chian gulf, causing mechanical deposit to take the place of 
