GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 133 



He who rejects this view of the imperfection of the 

 geological record will rightly reject the whole theory. 

 For he may ask in vain where are the numberless tran- 

 sitional links which must formerly have connected the 

 closely allied or representative species found in the suc- 

 cessive stages of the same great formation ? He may 

 disbelieve in the immense intervals of time which must 

 have elapsed between our consecutive formations; he 

 may overlook how important a part migration has played, 

 when the formations of any one great region, as those of 

 Europe, are considered; he may urge the apparent, but 

 often falsely apparent, sudden coming in of whole groups 

 of species. He may ask where are the remains of those 

 infinitely numerous organisms which must have existed 

 long before the Cambrian system was deposited ? We 

 now know that at least one animal did then exist; but 

 I can answer this last question only by supposing that 

 where our oceans now extend they have extended for 

 an enormous period, and where our oscillating continents 

 now stand they have stood since the commencement of 

 the Cambrian system; but that, long before that epoch, 

 the world presented a widely different aspect; and that 

 the older continents, formed of formations older than any 

 known to us, exist now only as remnants in a metamor- 

 phosed condition, or lie still buried under the ocean. 



Passing from these difficulties, the other great leading 

 facts in paleontology agree admirably with the theory of 

 descent with modification through variation and natural 

 selection. We can thus understand how it is that new 

 species come in slowly and successively; how species of 

 different classes do not necessarily change together, or at 

 the same rate, or in the same degree; yet in the long 



