XC PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I9II, 



its start. It is doubtful whether, in an}' case, we can go back 

 farther than tbe great Chalk covering for the initiation of the 

 earliest of our existent drainage-lines, and even drainage initiated 

 in Tertiary times has in many cases suffered serious modifications 

 during the latter part of that Era. 



(10) Earth-Movement and Life. 



There can be little doubt that a biological reflexion of the 

 changes in physical geography of even a small area like our own 

 country will be found in the progress of its life, if this is definitely 

 looked for by palaeontologists. Just as, locally at any rate, 

 unfavourable circumstances have certainly retarded or shifted the 

 direction of evolution, so the coincidence of a number of favourable 

 features must exercise a stimulating influence upon it. But the 

 case must necessarily be much complicated by the action of other 

 factors in the physical environment, and the reactions of organisms 

 upon each other. 



As an example, we may take the point made by Starkie Gardner 

 when he showed that one of the most potent factors in mammalian 

 development must have been the coming into existence of grasses 

 and herbage plants. These had a physical reaction upon the 

 formation of soil and in modifying the course and extent of 

 denudation, while biologically they gave a great impetus to the 

 development of the Herbivora. But the extensive development of 

 these plants coincided with, and was partly dependent upon, the 

 production of wide and suitable plains on which there could be 

 established savannahs replacing many of the forests and swamps. 

 Following on this came a fresh impetus to the development of 

 migratory habits associated with power of speed, which in its turn 

 gave an impulse to the evolution of animals of gregarious habits on 

 the one hand and of hunting habits on the other. 



There are two essays which, even at this late date, are well 

 worth considering in this connexion. One is the Presidential 

 Address delivered to this Society by Huxley in 1870, in which he 

 dealt with evolution in geological time and the relation of 

 successive faunas to one another. The other is a paper by Searles 

 Y. "Wood, Jun., published in 1862, 1 of the existence of which Huxley 

 was unaware when writing the Address just mentioned. 



In the latter the author endeavoured to supply a physical 

 explanation in the first place of the exaggerated development of 



1 Pbil. Mag. vol. xxiii, pp. 101-71, 269-82, 382-93. 



