84 MONOGRAPH OF DURA DEN. 



and trunks, passinsi; through several bands of shale and sand- 

 stone ; and to come to more recent times in the earth's history, 

 there is a remarkably curious record of a clump of petrified 

 trees in a rocky passage of the Cordillera in the Uspallata 

 rano-e of South America. Eleven of the trees are silicified, 

 and from thirty to forty are converted into coarsely crystallized 

 white calcareous spar ; the trunks are from three to five feet 

 in circumference, abruptly broken off and projecting several 

 feet above the ground. The sandstone in which they are 

 imbedded, and from which they must have sprung, has been 

 accumulated in successive thin layers around their stems, 

 retaining the impression of the bark, and now raised amid 

 enormous masses of volcanic rock seven thousand feet above 

 the level of the valley. 



"It required little geological practice," says Darwin, "to interpret the 

 marvellous story which this scene at once unfolded ;* though I confess I was 

 at first so much astonished that I could scarcely believe the plainest evidence 

 of it. I saw the spot where a cluster of fine trees had once waved their 

 branches on the shores of the Atlantic, when that ocean — now driven back 

 700 miles— approached the base of the Andes. I saw that they had sprung 

 from a volcanic soil which had been raised above the level of the sea, and 

 that this dry land, with its upright trees, had subsequently been let down to 

 the depths of the ocean. There it was covered by sedimentary matter, and 

 this again by enormous streams of submarine lava, — one such mass alone 

 attaining the thickness of a thousand feet ; and these deluges of melted stone 

 and aqueous deposits had been five times spread out alternately. The ocean 

 which received such masses must have been deep ; but again the subterranean 

 forces exerted their powers, and I now beheld the bed of that sea forming a 

 chain of mountains more than 7000 feet in altitude. Nor had those anta- 

 gonist forces been dormant which are always at work to wear down the 

 surface of the land to one level ; — the great piles of strata had been inter- 

 sected by many wide valleys, and the trees, now changed into silex, were 

 exposed projecting from the volcanic soil now changed into rock, whence for- 

 merly, in a green and budding state, they had raised their stately heads. Now 

 all is utterly irreclaimable and desert ; even the lichen cannot adhere to the 

 stony casts of former trees. Vast and scarcely comprehensible as such changes 

 must ever appear, yet they have all occurred within a period recent when 

 compared with the history of the Cordillera; and that Cordillera itself is 

 modern as compared with some other of the fossiliferous strata of South 

 America." 



* Journal of Rcscarclics, h\ Cliailcs Darwiu, Esi^., F.E.S., p. 40G. 



