GEOLOGY. 295 



rose through the destructive plane of the sea-level, both on their first emerg- 

 ence and tit subsequent periods, when, after depression, they have had again 

 to rise through that level. However great may have been the removal of 

 rock, therefore, from over what are now the crests of our mountains, it does 

 not follow that the mountains were ever materially loftier than they are now. 

 Not only were those vast sheets of rock removed by the action of the sea, but 

 the gaps and passes that indent the summits of mountains, as well as many 

 of the glens, ravines, and valleys that furrow their sides, were evidently com- 

 menced by the same action, though I am quite willing to believe that atmos- 

 pheric agency has deepened and widened, and sometimes produced, these to 

 a much greater extent than is commonly supposed. 



We certainly could not have any example of the elevation of a mountain 

 chain during historic times if, as I am fully convinced, any mountain chain 

 requires, not thousands, but millions, and even hundreds of millions, of years 

 for its elaboration. Sir C. Lyell has given us abundant proof that the two 

 actions of elevation and denudation, by which mountain chains have been 

 produced, are still going on with as much vigor and intensity as they ever 

 were. 



Furthermore, I would observe that while admiring the ingenuity of Sir 

 Henry's application of the hypothesis he favors to the production of such 

 structures as "faults" and "cleavage," there does not appear to be the 

 slightest necessity to evoke such a "dens ex machina" as a shift of the 

 earth's axis for the purpose, since they might all be caused by the local 

 movements which now take place, and seem always to have been taking- 

 place, in different parts of the earth's crust. 



Lastly, there is not any good evidence in favor of the supposition that 

 periods of tranquil deposition and periods of disturbance were ever common 

 to the whole globe. On the contrary, everything is in favor of the belief 

 that, during all geological time, tranquillity and disturbance have always 

 been simultaneous in different parts of the globe, just as they are now. 



That "whole races of animals and plants" have ever been " utterly and 

 entirely annihilated over the whole world," is a gratuitous supposition taken 

 up at one time by geologists from want of proper consideration of the facts 

 of the case. They unconsciously assumed a continuity of succession in the 

 deposition of the groups of strata which can never be proved, though, in 

 many instances, it can be disproved by evidence independent of the fossils. 

 I have often discussed this question with the late Edward Forbes and others, 

 and have arrived with them at the firm conviction that the change in the forms 

 of life inhabiting the globe may have always been as slow and gradual as 

 it has been during the historic period. We know that some species have 

 become extinct, not only for particular localities, but for the whole world, 

 even within the last few centuries. The introduction of new forms may have 

 been just as gradual. The appearance of sudden changes in the fossils 

 found in a vertical succession of beds is due to the fact of our having one 

 group of beds deposited during the middle, or end perhaps, of one great 

 geological period, i-esting directly on the undisturbed surfaces of another 

 group of beds belonging to some anterior period; nothing having been 

 deposited in that locality during the whole vast interval by which its lapse 

 could be recognized. 



My friend Sir Henry refers the production of the corrugation of the strata, 

 and that of the joints, faults, and cleavage, which traverse them, to the 

 shifting of the protuberant mass of the globe, and says that that shifting is 



