President's Address. 
197 
poraneous in formation with those of Europe, or that those 
either of Europe or America were synchronous with those 
of Australia. On the contrary, thousands of ages may have 
intervened between their depositions ; and all that we can 
attempt, or philosophically are permitted to attempt, is co- 
ordination in fossil forms and similarity of conditions, but 
not co-ordination in time or synchrony of formation. Take, 
for illustration, the post-glacial beds of the Clyde, that con- 
tain certain species of shells now extinct in the latitudes of 
Britain, but which still flourish in the seas of Greenland. 
The post-glacial era is separated from the present by an 
immense lapse of time ; and yet, were the muds of the 
Greenland seas and the clays of the Clyde presented to 
future palaeontologists, they might, according to the prac- 
tice of co-ordinating by species, be regarded as contempo- 
raneous, Nothing, however, could be further from the 
truth ; and so nothing is more likely to be erroneous than 
many of the contemporaneities that have been attempted 
by geologists. In the very nature of thingSj few species 
can have a world-wide distribution ; the spread of plants 
and animals from their specific centres is slow and gradual ; 
and the oscillations of sea and land that produce these ex- 
ternal conditions, favourable or unfavourable to the geogra- 
phical transference of life, are also extremely gradual. As 
in dealing with the problems of physical geology we reason 
from the present to the past, so in dealing with organic 
questions we must reason, in like manner, from the existing 
to the extinct. At present, no two regions present the 
same specific facies, and we are not to presume that any 
other order prevailed in bygone ages. If we argue for 
uniformity in the forces of nature, we can scarcely refuse 
to admit a similar uniformity in her metlwds. According 
to this doctrine, each area in time must have been peopled 
by its own specific forms ; and, as at the present day, differ- 
ent species may be entombed in widely-separated deposits, 
which are strictly synchronous, so in former epochs, as 
has been well remarked by Professor Huxley, " absolute 
diversity of species is no proof of difference of date, just as 
absolute identity can be no evidence of contemporaneous 
