624 C. Darwin, Esq., on Volcanic 



recent period, so, as certainly, must masses on the lines of fracture have been 

 unequally lifted up and let down, — that is, some steps in the formation of a 

 mountain-chain have been produced. 



I may here ask, when Mr. Hopkins* says, he " can in no way conceive the 

 successive formation of parallel fissures, without hypotheses respecting the 

 mode of action of the elevatory force, which are infinitely too arbitrary to be 

 admitted for an instant," has he considered the effects of long intervals of 

 rest, during which the injected rock might become solid ? Would not the 

 crust in such case yield more readily on either flank, as I believe it must have 

 done in the Cordillera, than on the line of an axis composed of solidified rocks, 

 such as granite or porphyry .? An extremely slow elevation of the land, with 

 long intervals of rest, being the only kind of movement of which we have 

 any knowledge, the slow cooling of that portion of the liquefied rock which is 

 propelled into the upper parts of the crust, cannot be considered an arbi- 

 trary assumption. 



From the facts stated in this paper, we may safely conclude, that volcanic 

 action, even on a veri/ grand scale, as in the Andes, is only one effect of the 

 power which elevates continents, at the slow rate at which the South Ame- 

 rican coast is now rising. In looking back to the past history of the world, we 

 learn from Mr. Lyellf, that there have been volcanic eruptions during every 

 epoch, from that of the Cambrian formations to the present day. The ancient 

 eruptions seem to have been accompanied by all the circumstances which 

 attend modern ones ; nor is there any evidence, as remarked by the same au- 

 thor, that the quantity of matter ejected, in the greater number of ancient cases, 

 was excessive. Therefore, we must conclude that continental elevations, one of 

 the effects of the same motive power which keeps the volcano in action, has 

 ordinarily gone on, since those ancient days, at the same slow rate as at pre- 

 sent, and, consequently, as above inferred, the step-like formation of moun- 

 tain-chains. It may, therefore, be questioned, whether we are justified in 

 admitting the hypothesis of a paroxysmal elevation of any mountain-chain, 

 without distinct proofs in each particular case, that a series of impulses, like 

 those, which now acting frequently on the same lines, rend the earth's crust, 



* Abstract of a Memoir on Physical Geology, by W. Hopkins, Esq., M.A., p. 31. 



f Elements of Geology. In the 24th chapter, Mr. Lyell has collected instances of volcanic 

 eruptions in each of the great epochs of the geological history of Europe. The argument, which 

 follows in the text, is the same with that advanced by this author in the Principles of Geology, 

 (Book I. Chap, v.) but Mr. Lyell more particularly applies it to the earthquakes and convul- 

 sions, " caused by subterranean movements, which seem to be merely another portion of the vol- 

 canic phenomena." 



