Qn (he Comparative Level of lakes and Seeis. 32.7 



and always excluding Lake Aral, — more than 18,000 square marine 

 leagues ; in other words, a surface of 900 square leagues larger than that 

 of France. It is earnestly to be wished that the Imperial Academy of 

 St Petersburg will continue the beautiful geodaesical survey commenced 

 under its auspices, and that that illustrious society will not only ascertain 

 the true difference of the heights of the Aral and the Caspian, but that, 

 so far as these regions are accessible to such peaceful occupations, they 

 will also succeed in procuring the zero geodmical line between he Volga 

 and the laik, between the lai'k, the Emba, and the north-east extremity 

 of the Aral Sea, and finally, between this sea and the Aksakal-Barbi * 



M. Arago who, in his writings, always ascends with success to first prin- 

 ciples concerning the physical constitution of the globi, haSj in his memoir 

 upon comets, pointedout a curious work of HaUey,t in which the English 

 astronomer, as eai'ly as December 1G94, mentioned the c/rcat depression of 

 the Caspian, which he attributes to the shock of a ball of immense dimen- 

 sions; in other words, of a comet. "The vast depression," observes M. 

 Arago, "ofa whole country, in formertimes appeared ofan explanation too 

 difficult for the action of any ordinary forces ; and in despair of such 

 causes, recourse was had, as in many other circumstances, to an action pro- 

 ceeding from the celestial spaces. In the present state of our geological 

 knowledge, this idea of Halley will not receive much favour. Scarcely any 

 one now doubts that the isolated peaks, and the longest and most eleva- 

 ted ranges of mountains, have proceeded from the interior of the globe 

 by the way of upheaving. But does not this very upheaving imply the 

 production of a void beneath the surrounding districts, and the possibi- 

 lity of this subsequent subsidence .'* "When we cast our eyes upon a 

 geographical chart, we easily perceive that no part of the world exhibits 

 so many upraised masses as Asia. Around the Caspian Sea, at greater 

 or less distances, we find the high lands of Iran and of Central Asia, the 

 mountain chains of Kouen-lun, and of Hindoo-Kho, the mountains of 



and Behaghel, the Volga near Zaritzin is 27 toises lower than the Don 72 versts 

 above the Patiisbansk. I assign these valuations, remembering how uncertain a 

 barometric levelling is in the plains and for the measurement of small heights, 

 when the differences in the height of the columns of mercury do not attain to 

 2 millimetres, and arc grounded upon a small number of observations. 



* I attach great importance to the determination of the height of the land in 

 the Steppe, which the ancient hollow, running S.S.E. and N.N.E., and of which I 

 have often spoken, follows. I find in my correspondence with M. St Martin, that 

 this sa/vant had heard of " a tradition of the Avares, according to which this people 

 allege that they had quitted their original place of abode (at the foot of Altai ?) 

 on account of the sudden drying up of an interior sea, and of an increased dryness 

 of the Steppe." I am quite ignorant of the source whence M. St Martin pro- 

 cured this notice, which we might be tempted to associate with the Chinese story 

 of the disappearance of the " Sea of bitter waters." 



t Some consi'.Urationa about the cause of the Universal Deluge, Phil. Trans, vol. 

 xxxiii. p. 122. " A shock of a comet may have occasioned that vast depression of 

 the Caspian Sea and other great lakes in the world." 



