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On the principal Geological Phenomena of the Caucastts and tlie 

 Crimea. In a Letter from M. F. du Bois, to M. Elie ixe 

 Beaumont. 



M. Du Bois has discovered several epochs of (soulevement) 

 elevation in the region of the Caucasus. The oldest of these 

 which he has clearly recognised, is posterior to the Jura forma- 

 tion, which of course has participated in the convulsion. Granitic 

 masses, he remarks, have pierced the thick mass of black schist, 

 and have dislocated it, in heaving aside ilic strata of Jura lime- 

 stone, which were superimposed, and thus bursting the crust of 

 the earth have raised from the depths of the ocean the first rudi- 

 ments of what might be called the island of the Caucasus, and 

 which was elevated several thousand feet above the level of the 

 surrounding sea. An epoch of repose succeeded to this first 

 cataclysm, and sedimentary deposits followed the first uprising. 

 During this period of repose, the lower schist of the chalk and 

 the green-sand were calmly deposited. Each of these stages 

 of deposit produced a formation of many thousand feet in thick- 

 ness. The conclusion of the epoch of the green-sand, appears 

 to have been marked by a new upraising, viz. that of the Ak- 

 altsikhe chain, the axis of which approximates in its direction to 

 that between east and west, very nearly corresponding to that 

 of the elevation of the sandstone and the marl in the Carpathian 

 chain. 



The principal agent, in this new revolution, was mela- 

 phyre, or pyroxenous porphyry ; it has cleft the chain in the 

 greater part of its length, and has broken forth by this gap, 

 turning aside on either side the two slopes of the chalk, under 

 an angle of 30°, more or less, not at all unlike the roof of a 

 house. This circumstance may very readily be observed in the 

 journey from Koutais to Akaltsikhe, across this range, which is 

 nearly 10,000 feet high. 



After this second upraising, there existed, according to M. du 

 Bois, between the Caucasian island already referred to, and the 

 Akaltsikhe range, a frith or sea, into which was deposited true 

 thalk, along with all its characteristic fossils, and to which there 



