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 things, 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 methods. 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 arc 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 



