EPOCH OF REVOLUTIONS. 357 



It was then they produced cracks in this crust, and filled CirAPTER 

 them not only with dykes, but with shapeless masses of ^^^"^' 

 matter of great density, such as ferruginous basalts, 

 greenstones, and masses of metal, materials which were 

 introduced subsequently to the solidification and flatten- 

 ing of the planet. The epoch of great geological revolu- Period of 

 tions, was that when the communication between the "'^''°"- 

 fluid interior of the earth and its atmosphere were the 

 most frequent — when they acted upon a greater number 

 of points — when the tendency to establish these commu- 

 nications lias upheaved, (at different epochs, and by dif- 

 ferent kinds of action), upon long crevices, — Cordilleras, 

 like the Himalaya and the Andes, or chains of moun- 

 tains of less elevation, or finally those ridges and heights 

 whose varied undulations embellish the landscape of our 

 plains. It is as the witness of these upheavals, and mark- Relative ngo 

 ing (after the grand and mgenious views of JVl. Elie de tains. 

 Beaumont) the relative age of the mountains I have seen 

 in the Andes of the New world, at Cundinamara; — of ex- 

 tensive formations of grit, stretching oyer the plains of 

 Magdalena and Meta almost uninterruptedly, in plateaus 

 about 9000 feet high, that I have found still more re- 

 cently in the north of Asia, in the chain of the Ural, the 

 same bones of antediluvian animals, (so celebrated in the Bones of 



1 • ^iT^ iiTis-i antedilnviau 



lower regions of the Koma and the Irtyche), mixed on animals, 

 the back of the chain, and in the j^lateaus between 

 Beresovsk and Ekaterinbourg with earths rich in gold, 

 diamonds, and platina. It is also as a witness of the 

 subterranean action of elastic fluids which raise conti- 

 nents, mountain chains, and insulated domes — which 

 displace rocks, and the organic debris which these rocks 

 contain — which produce heights or hollows as the vaults 

 crumble down, that we ought to consider the prat de- 

 pression which the west of Asia presents to us. The sur- Area of 

 face of the Caspian Sea, and of the Lake Aral, forms ^'=P'e^='°"' 

 the lowest part of it ; but the depression extends itself 

 far into the interior of the country beyond the Sarepta, 

 as at the Lake of Elton, aud at the steppes of Bogdo, be- 



Y 



