ANNIVERSARY ADDRESS OF THE PRESIDENT. lvl 
necessarily founded on the physical or zoological changes or modifi- 
cations which have been effected upon it, and it were well, often, if 
these classifications took so wide a range and were not extended from 
minor portions of that area. The study of a limited district is fre- 
quently sufficient to place us on our guard against a too partial re- 
gard for subdivisions ; the modification of physical conditions, and 
with them, allowing for a great adjusting power, of contemporaneous 
life, pressing upon our attention. True it, no doubt, is that, as 
regards temperature only, molluscs and other marine creatures may 
find the needful limits within which they can sustain life very exten- 
sively in the sea, the waters adjusting themselves to the specific gra- 
vities due to their relative heat. So long therefore as finding proper 
food, they can battle against changes of pressure from differences of 
depth, modifications of sea-bottom, of light passing through the waters, 
and of distances from shores, many species might contend through 
these difficulties and thus spread themselves contemporaneously over 
considerable areas. At the same time, this power of adjustment 
would enable them to live through changes of a similar physical cha- 
racter brought about within a limited area. This now seems a well- 
established opinion among paleontologists, who regard the species 
most widely spread at a given period as those which existed through 
the greatest length of geological time. 
On this head Mr. Sharpe remarks that the comparison of the 
palzeozoic fossils of Europe and of the United States bears out the 
view that those species which rise through the greatest thickness 
of formations have also the widest geographical range. ‘‘ We find 
in New York,”’ he observes, “‘ European species, which are confined 
here to a single bed, as well as those which are common to several 
formations, and usually the species seem to have the same vertical 
range in both countries.”” Of this Mr. Sharpe enumerates some ex- 
amples, stating that they could readily be multiplied, and he points 
out the importance of endeavouring to ascertain m different countries 
the first appearance of each species, seeing whether it is found in one 
at an earlier geological period than in another, and thus to learn the 
region of which it was originally native. Respecting this he also men- 
tions facts which he considers may tend to show that Spirifer Urii 
appeared earliest upon the area now occupied by North America, as 
also Terebratula reticularis, and Orthis resupinata. On the other 
hand he remarks that, when observations are more multiplied, and 
we discover certain species to have first appeared upon the European 
area, Leptena depressa may perhaps be found among them. Mr. 
Sharpe remarks that if, without regarding species, we look only to 
general forms, we shall find some groups of shells common in the 
United States long before they lived in the European area. 
Viewing all the causes of modification and change in physical con- 
ditions at equal dates and during the lapse of a certain amount of 
geological time, and the power of marine life to adjust itself to 
certain of these changes and modifications, as well contemporaneously 
as during such lapse of time, by no means neglecting the great 
changes in animal life so evident when we look at its remains en- 
