PALEONTOLOGY OF NEW-YORK. 
62 
of shallow water the land-derived materials and the low lands themselves 
were pushed farther to the westward, encroaching upon the ancient sea : 
at other times the marine influences and marine deposits prevailed, and 
the soft and finely comminuted material spread over the bottom was 
mingled with the exuviae of marine animals, forming a calcareous shale 
or an argillaceous limestone. The presence of this ocean is marked in 
Eastern Ohio by a band of limestone several feet in thickness, containing 
marine shells of the same species which prevail more abundantly and 
through a much greater thickness of calcareous strata in Iowa and Missouri. 
The accumulation of such a bed of limestone, made up in large proportion 
of the exuviae of marine animals, could only have been made during a 
quiet interval, when the surface was submerged to a considerable depth, 
and while there was no influx of shore-derived materials. 
The calcareous matter goes on increasing westward; the marine fauna 
becomes more and more abundant, until we find ourselves gradually leaving 
the shore-derived materials, and coming among those which are wholly 
of marine origin. In the same proportion the characteristic feature of the 
formation, the coal, will be found to diminish, and we must be prepared tp 
learn that the productive portion of the Coal measures do ultimately give 
place, in great part or entirely, to the marine portions of the formation, 
which increase towards the west in force and importance. 
To my own view, we find in the Coal measure formation the culmina¬ 
tion of that order of things which commences with the Hamilton group, 
was expressed but feebly in the beginning, but growing stronger and 
stronger through the Portage, Chemung and Catskill-mountain periods, 
finds its full expression in the Coal period. 
But even this condition, gradually initiated, long continued, and wide 
spread as it is on this continent, is not the universal expression of that 
period in the geological history of the world. Nor is this peculiar flora, 
existing through so long a period, and widely distributed as it is, to be 
regarded as the universally marked period of plant life. It so happens that 
from the stand-point which we occupy, this feature is more strongly 
impressed, and more widely and fully expressed than any other which we 
