ORIGIN OF SPECIES 4-03 



supplied the broken Hints for the formation of so much gravel 

 at various heights, sometimes 100 feet above the present level 

 of the Somme, for the deposition of fine sediment including 

 entire shells both terrestrial and aquatic, and also for the 

 denudation which the entire mass of stratified drift has under- 

 gone, portions having been swept away, so that what remains 

 of it often terminates abruptly in old river cliffs, besides being 

 covered by a newer unstratified drift. To explain these 

 changes, I should infer considerable oscillations in the level 

 of the land in that part of France ; slow movements of up- 

 heaval and subsidence, deranging but not wholly displacing 

 the course of ancient rivers. Lastly, the disappearance of the 

 elephant, rhinoceros, and other genera of quadrupeds, now 

 foreign to Europe, implies in like manner a vast lapse of 

 ages, separating the era in wdiich the fossil implements were 

 framed, and that of the invasion of Gaul by the Bomans."* 



As to the successive appearance of new species in the 

 course of geological time, it is first requisite to avoid 

 the common mistake of confounding the propositions, of 

 species being the result of a continuously operating second- 

 ary cause, and of the mode of operation of such creative cause. 

 Biologists may entertain the first without accepting any cur- 

 rent hypothesis as to the second. 



That the species of the mineralogist and the botanist should 

 be owing to influences so different as is implied by the opera- 

 tion of a second cause, and the direct interference of a first 

 cause, is not probable. The nature of the forces operating in 

 the production of a lichen may not be so clearly understood as 

 those which arranged the atoms of the crystal on which the 

 lichen spreads. Pouchet has contributed the most valuable 

 evidence as to the fact and mode of the production by external 



* Address, on opening the Section of Geology, at the Meeting of the British 

 Association at Aberdeen, September 15,-1859. 



