8 EARLY MAN IN BRITAIN. [CHAP. i. 



Darwin, that while the conditions of life were ever 

 changing, those animals and plants which were not 

 sufficiently plastic to conform to a new state of things 

 died out, while those which were more capable of modi- 

 fication, so as to be in harmony with their surroundings, 

 became what we know as new species, genera, families, 

 orders. 



Breaks in the Succession accompanied by 

 Geographical Changes. 



The succession of living forms has been uninterrupted, 

 although, from errors of observation, as well as from the 

 fragmentary nature of the evidence, it appears to be 

 broken. Each break may be likened to places from 

 which pages, or chapters, or whole volumes, as the case 

 may be, have been torn out from the record by the 

 hand of time, or not yet discovered by man. It must 

 also be observed that the breaks in the succession are 

 invariably accompanied by geographical change of cor- 

 responding magnitude. That, for example, which took 

 place at the close of the Secondary period consisted in 

 the elevation of the chalk rocks, which were accumulated 

 at the bottom of the Cretaceous ocean, extending from 

 southern and eastern Britain, through France into the 

 Mediterranean area, Greece, Palestine, Asia Minor, 

 Germany, Eussia, and far into Asia, so as to form a 

 continent on which the Eocene mammalia make their 

 appearance. In this case the conditions of life must 

 have been profoundly modified by the geographical 

 change. The climate must have been altered, and forms 

 of life, which had been previously elaborated outside 

 Europe, would enter into competition with the old 



