Devonian Era in the Ohio Basin. — Clay pole. 33 
iod, even in New York. At the same time, the occurrence of so 
great changes both in stratigraphy and in palaeontology proves 
with equal clearness and force that some great physical and 
geographical change took place requiring, we may say com- 
pelling, coincident or consequent equivalent modification in the 
living forms of the region on pain of quick extinction. 
The nature of the Hamilton strata in their different out- 
crops indicates plainly in what direction it is necessary to look 
for the physical cause of the transition. The prevalence of 
• mechanical deposits in the east is unmistakable. The well 
known sandstone quarries in Kingston, Saugerties and other 
places on the Hudson river prove that erosion was active in the 
northeast. The massive sandstone of Middle Pennsylvania is 
equally decisive in that direction. The shales of the group 
speak with clearness of eastern elevation as far south as south- 
ern Pennsylvania. To the westward the diminishing mass of 
these sediments and the increase in the proportion of theic 
calcareous ingredients bespeak conclusively the absence of dry 
land in that quarter. The eastern seaboard is, then, the place 
in which the source of this new revolution must be sought — 
the same region from which some of the earlier movements 
have been found to issue. In palaeozoic time, as in later days, 
man}- of the great epochal forces of the country have mani- 
fested themselves first near the Atlantic coast, but their effects 
have been felt long and far to the west. 
Features in Ohio. — The clear and definite boundaries of the 
Corniferous-Hamilton found in the typical area do not exist in 
Ohio, and there has been, in consequence, no little controversy 
regarding the dividing plane between them and, indeed, regard- 
ing the very existence in the state of the later stratum. This 
will be obvious on reference to the "Geology- of Ohio," in which 
most of the various views on the subject have been recorded 
and discussed. 
These opinions sufficiently show that great hesitation was 
felt by those who studied the so-called Corniferous limestone 
of Ohio in assigning the whole mass to that group. The oc- 
currence of common, even if not characteristic, Hamilton spec- 
ies far down in the limestone and of Corniferous fossils above 
them indicates a considerable deviation from the fauna of the 
typical area in New York. 
