ANNIVERSARY ADDRESS OF THE PRESIDENT. lv 
whence they are obtained into three great groups, considered as dis- 
tinguishable as well by their lithological structure as by their zoo- 
logical character. The lowest is a vast arenaceous accumulation, 
with occasional beds of limestone, and includes the lowest fossiliferous 
rocks in the ascending series up to the Medina sandstone. The 
molluses discovered in this division are stated to present a great 
accordance with those in the Lower Silurian rocks of Europe, in this 
view including the Clinton beds. 
The next group is calcareous, with some associated sandstones 
and shales, and commencing with the Niagara shale ends with the 
upper Pentamerus limestone, according to Mr. Conrad, or according 
to the views of Mr. Hall, with the corniferous limestone. This group 
is considered equivalent to the Upper Silurian series of Europe. The 
third, or upper group, consisting chiefly of shales and argillaceous 
sandstones, reaches upwards to the top of the Chemung beds, and is 
referred to the geological date of the Devonian or Carboniferous systems 
of Europe, or rather to an enormous development of the former. 
In the lowest group about 30 per cent. of the species of molluscs 
agree with those known in the Lower Silurian rocks of Europe ; in the 
second, or middle group, 40 per cent. of the species are the same 
with those detected in the Upper Silurian rocks on the eastern side 
of the Atlantic; and, in the highest group, 20 -per cent. of species 
agree with those found in the Devonian or carboniferous series of 
Europe. To these numerical calculations of species Mr. Sharpe 
attaches, however, little importance, believing the sources of error in 
such calculations to be alike numerous and varied, and that collections 
must be far more extended, and comparisons made with greater care » 
before they can be regarded as valuable. 
No one is more aware than Mr. Sharpe of the difficulties attending 
even the larger grouping of fossiliferous accumulations, far distant 
from each other, or of the necessity of viewing the limits of the divi- 
sions above noticed as somewhat hypothetical. Indeed, when we 
consider the. probable physical conditions under which the mineral 
matter was accumulated in which the older organic remains noticed on 
both sides the present Atlantic are discovered, the necessity of great 
caution on this head becomes apparent. We must, of course, dismiss 
from our minds the present geographical distribution of sea and land, 
extending from and including Europe and North America. The 
many rises and depressions of land which the study of geology teaches 
us has since happened within the areas in Europe and North America 
now above the sea, show how needful this must be. Moreover great 
disturbances of the earth’s crust, producing crumplings, flexures, and 
fractures, round and against which subsequent accumulations were 
effected, have taken place since the deposit of these older rocks. 
Whatever the form of the ancient lands whence the mineral mate- 
rials of the older paleeozoic rocks were derived, we have a given 
general distance on the surface of the globe always interposed between 
the deposits. When we regard any extended line of coast along 
the shores of our present continents, and, therefore, conditions in 
the seas adjoining most favourable, generally, for continued similar 
