XIII 
THE GEOLOGICAL EVIDENCES OF EVOLUTION 
3S1 
record of all the species that have existed since the two forms 
began to diverge from their common ancestor, and this the 
known imperfection of the record renders it almost impossible 
that we should ever attain. All that we have a right to 
expect is, that, as we multiply the fossil forms in any group, 
the gaps that at first existed in that group shall become less 
wide and less numerous; and also that, in some cases, a tolerably 
direct series shall be found, by which the more specialised 
forms of the present day shall be connected with more 
generalised ancestral types. We might also expect that when 
a country is now characterised by special groups of animals, 
the fossil forms that immediately preceded them shall, for the 
most part, belong to the same groups; and further, that, com¬ 
paring the more ancient with the more modern types, we 
should find indications of progression, the earlier forms being, 
on the whole, lower in organisation, and less specialised in 
structure than the later. Now evidence of evolution of these 
varied kinds is what we do find, and almost every fresh discovery 
adds to their number and cogency. In order, therefore, to show 
that the testimony given by geology is entirely in favour of 
the theory of descent with modification, some of the more 
striking of the facts will now be given. 
Geological Evidences of Evolution. 
In an article in Nature (vol. xiv. p. 275), Professor Judd 
calls attention to some recent discoveries in the Hungarian 
plains, of fossil lacustrine shells, and their careful study by Dr. 
Neumayr and M. Paul of the Austrian Geological Survey. 
The beds in which they occur have accumulated to the thick¬ 
ness of 2000 feet, containing throughout abundance of fossils, 
and divisible into eight zones, each of which exhibits a well- 
marked and characteristic fauna Professor Judd then de¬ 
scribes the bearing of these discoveries as follows— 
“ The group of shells Avhich affords the most interesting 
evidence of the origin of new forms through descent with modi¬ 
fication is that of the genus Vivipara or Paludina, which occurs 
in prodigious abundance throughout the whole series of fresh¬ 
water strata. W T e shall not, of course, attempt in this place 
to enter into any details concerning the forty distinct forms of 
this genus (Dr. Neumayr very properly hesitates to call them all 
