628 C. Darwin, Esq., on Volcanic 



angles would suffer, nor for the denudation and rounding of the upper ones. 

 This supposed crushing together of such gigantic fragments will, perhaps, 

 explain the utter confusion, which must be familiar to every geologist who 

 has examined any great mountain-chain*. I must here add, that according 

 to these views, which I believe are correct, the theoretical part of the fore- 

 going argument, namely the difficulty of confining during any paroxysmal 

 movement the fluid matter within the crust, is weakened ; yet I believe the 

 principle holds good, for, in order to break up and throw over portions of very 

 thick crust, as in Diagram 3, there must have been great horizontal extension, 

 and this, if sudden, would have caused as many continuous outbursts of vol- 

 canic matter, as there now are axes of solid rock. Moreover, when we con- 

 sider, first, that the fragments must have stood for one instant separate from 

 each other, and, secondly, that the force necessary to turn over and crush to- 

 gether at one effort these immense masses, must have been in proportion 

 enormously great to that required merely to lift them, — it cannot, I think, be 

 doubted for a moment, that if the force had acted suddenly, these portions of 

 the earth's crust would have been absolutely blown off, like fragments of rock 

 by gunpowder ; but this has not happened, and, therefore, the force did not 

 act suddenlyf . 



If we grant that the earthquake of Concepcion on the 20th of February 

 marked one step in the elevation of a mountain-chain ; then, as during the 

 twelve succeeding days there were counted upwards of three hundred shocks, 

 which proceeded from the same quarter with the great shock, so the fluid stone 



* In the Cordillera, the axis of plutonic rock is less exposed in the principal, than in the subor- 

 dinate lines ; some strongly marked exceptions, however, occur. In the former, also, the strata 

 are most inclined. As, according to the views here advocated, the formation of a mountain-chain 

 is due to innumerable impulses, the highest part must generally have felt the greatest num- 

 ber of impulses, and therefore its stratification would generally be most disturbed. And if a 

 great part of the disturbance be due to the lateral force resulting from the compression of the 

 great thick portions of the earth's crust, then the central lines, or those which have several ridges 

 on both sides of them, would be most crushed together, and consequently the strata would be 

 most closely packed over them. I can understand on no other principle, the circumstance of the 

 rock of the axis being visible not on the loftiest, but on the secondary lines of a mountain-range, 

 which very frequently occurs. 



•}• Mr. Hopkins moreover argues, (Abstract of a Memoir on Physical Geology, p. 15,) that if 

 the elevatory force had the character of an impulsive action, it " would produce the most irregular 

 phenomena, and such as would be altogether without the sphere of calculation, I exclude, there- 

 fore, the hypothesis of this kind of action, not as involving in Itself any manifest improbability, 

 but as inconsistent with the existence of distinct approximations to general laws in the resulting 

 phenomena." In other parts the author shows that such approximations do exist in nature. — See 

 also Phil. Mag. 1836, Vol. viii. p. 234. 



