recently carried on in the Russian Empire. 299 



of Orenburg due to MM. Hoffmann and Helmersson, a level- 

 ling by station made by the same observers with the aid of a 

 barometer, from Orenburg to Gourief, the east part of the^ 

 Caspian Sea; corresponding measures taken during several 

 months in these two places ; and lastly, observations which we 

 have recently made at Astrakhan and at the embouchure of the 

 Volga, corresponding at the same time to Sarepta, Orenburg/ 

 Kasan, and Moscow, will serve (when all the data are united 

 and rigorously calculated) to verify the absolute height of this 

 interior basin. 



On the north side of the Caspian every thing at present ap> 

 pears to indicate a progressive depression of the level of its 

 waters ; but without placing too much trust in the relation of 

 Hanway (an old English traveller, otherwise very estimable) 

 respecting its periodical increase and decrease, we cannot deny 

 the encroachments of the Caspian on the side of the ancient 

 town of Terek, and to the south of the embouchure of the Cyrus, 

 where scattered trunks of trees (the remains of a forest) are 

 found constantly inundated. The small island of Pogorelaia 

 Plita, on the contrary, seems to increase and rise progressively 

 above the waves which covered it a few years ago, before the 

 jet of flames which navigators perceived at a distance. 



In order to solve completely the great problems relative to' 

 the depression, perhaps variable, of the level of the sea and 

 that of the continental basin of the Caspian, it would be de- 

 sirable to trace in the interior of the land round this basin, in 

 the plains of Sarepta, Ouralsk, and Orenburg a ligne de 

 sonde^ by uniting the points which are exactly on the level of 

 the Baltic and the Black Sea, which will be compared with' 

 marks placed on the coast in the whole circuit of the Caspian, 

 (like the marks placed almost a century ago on the Swedish 

 shores by the Academy of Stockholm) if there is a general or 

 partial, a continued or a periodical depression of its waters, or 

 if rather (as has been conjectured for the whole of Scandina- 

 via, by that great geognost, M. Lepold de Buch,) a part of the 

 neighbouring continent is raised or depressed by volcanic causes^ 

 acting at immense depths in the interior of the globe. The 

 mountainous isthmus of the Caucasus, composed partly of 

 trachyte and other rocks, which owe their origin to volcanic fire. 



