378 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



genera, and species of the earlier ages gradually became ex- 

 tinct and were replaced by those of to-day. 



But whereas Cuvier, Agassiz, D'Orbigny, and other sup- 

 porters of the Catastrophal Theory had supposed the faunas 

 and floras of any one geological period to be sharply defined 

 from those of the foregoing and succeeding ages, and in fact 

 to have no species in common, Bronn insisted that a smaller 

 or larger number of genera and species passed from one age 

 to the next, and have been in a measure connecting intermediate 

 links. The creation of new types and the extinction of old 

 types had not been confined to a few "days" or "periods" 

 of creation associated with great earth catastrophes, but had 

 been continually and quietly going on as a consequence of the 

 changes in the external conditions of existence which had 

 been likewise continuously in progress during the whole 

 geological history of the earth. At the same time Bronn 

 allowed that certain surface changes had been the cause of 

 more far-reaching variations of form than others. The period 

 of existence that had been assigned to the fossil species was 

 extremely unequal ; as a rule, however, it had been very long. 

 The limits of the geological horizons, formations, etc., are 

 neither in palaeontological nor in geographical or lithological 

 respect absolutely sharp, but are frequently more or less in- 

 definable. 



The able arguments of Bronn opened up a series of ques- 

 tions which until his time had either been entirely neglected by 

 palaeontologists, or had never benefited by a frank and lucid 

 expression of their difficulties. Bronn's teaching was in close 

 harmony with Charles LyelPs doctrine of the uniformitarian 

 development of the earth ; more especially Bronn's insistence 

 upon the continuity in the processes of change, and his scien- 

 tific demonstration of transitional species and genera bridging 

 the supposed gaps in the palaeontological and stratigraphical 

 succession provided a stepping-stone for the acceptance of 

 Darwin's grander principles. When, in the year 1859, Darwin's 

 epochal work On the Origin of Species by means of Natural 

 Selection appeared, it was Bronn who was one of the first in 

 Germany to recognise it as the outcome of an extraordinary 

 genius, and he immediately translated the work into the 

 German language. 



The publication, in 1866, of Ernst Haeckel's work on 

 General Morphology was the first practical application of 



