OPERATION FROM THE ELEVATION OF MOUNTAINS. 343 



beds of limestone, supposed to be marine, and a few marine organic 

 remains. In such situations we must admit, that the lakes or basins 

 in which the coal strata are deposited, were nearly on a level with 

 the sea, and subject to occasional irruptions of salt water ; or the rel- 

 ative level of the land and sea may have been changed, by frequent 

 oscillations of the land. The strata of coal and ironstone are much 

 too regularly separated from admixture with other substances, to al- 

 low us to suppose, that they were formed by matter drifted into the 

 sea. If the regular coal strata in our English coal fields are not 

 freshwater formations, deposited in marshes or in tranquil water, we 

 can have no evidence for freshwater formations in any part of the 

 world. All the coal basins were either formed in inland marshes or 

 lakes, or were surrounded by dry land ; but a great submergence of 

 the land took place, and they were covered in many parts by thick 

 depositions of marine limestone. At a subsequent period, they again 

 emerged from the ocean with a covering of marine secondary strata. 

 (See Appendix.) It would not be difficult to accumulate proofs, of 

 the repeated elevation and submersion of portions of the crust of the 

 globe. 



The following account is interesting, from the vast extent of sur- 

 face to which it relates ; but it may be said to piesent rather a de- 

 scription of the present state of the earth's surface, than a direct 

 proof of former changes. M. Humboldt, in a recent work, entitled 

 Fragmens Geologiques sur V Asie Ceritrale, the result of his late 

 travels into Asia, observes, that the high part of central Asia, com- 

 monly called le grand plateau, is composed of four powerful ranges 

 [sysiemes) of mountains, directed east and west, and supported by a 

 common base, also raised above the surrounding country. At the foot 

 of this immense system of mountain chains and elevated ground, is 

 an enormous depression, eighteen thousand miles square, and froos 

 150 feet to 300 feet below the level of the ocean. The surface of 

 the Caspian Sea and the level of Astracan is 300 feet lower than the- 

 sea, and the course of the Volga is 150 feet lower. M. Humboldt 

 supposes, that this subsidence was the result of the elevation of the 

 Plateau, which supports the Himalaya and Irun mountains, and per- 

 haps those of Caucasus, an enormous mass, the elevation of which 

 can be compared to no geological phenomena of the same order, ob- 

 served on the other continents. 



M. Humboldt notices the existing traces of volcanic agents in cen- 

 tral Asia, which may be more or less directly connected with the 

 internal force, that has produced such mighty results. 



The epoch of these elevations is not precisely indicated by M. 

 Humboldt, but the discovery of tertiary shells in the higher regions 

 of Caucasus and the Himalaya mountains, analogous to those in the 

 adjacent seas, may lead us to regard the elevation of these mountain 

 chains, as being posterior to the latest tertiary epoch, which would 

 (if established) confirm the conclusion, " that the highest chains of 



