XIII THE GEOLOGICAL EVIDENCES OF EVOLUTION 381 



record of all the species that have existed since the two forms 

 began to diverge from their common ancestor, and this the 

 kno^vn 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 Avhich the more specialised 

 forms of the present day shall be connected with more 

 generalised ancestral types. We might also expect that when 2 . 

 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 \nth. the more modern types, Ave 3 

 should find indications of progTCssion, 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 which 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. We shall not, of course, attempt in this place 

 to enter into any details concerning the forty distinct fmins of 

 this genus (Dr. Neumayr very properly hesitates to call them all 



