330 On the Comparative Level of Lakes and Seas. 



the Euxine to the Caspian Sea.*"^ This strait must have produced a 

 marine current from west to east, similar, on a small scale, to that which 

 issues by the pillars of Hercules into the Mediterranean, and which 

 may be traced even to the coast of Pelusium, where it opposes the too 

 rapid increase of the Delta of Egypt, t 



Without having recourse to the oscillations which, at the epoch of 

 great geological revolutions, have made the recently solidified crust of 

 our planet often rise and fall in the plains, we may suppose that, even 

 still, many continental regions, supported by solid rocks, are found at a 

 level inferior to that of the ocean, but that, from the large accumulation 

 of abraded soil, superimposed upon the tertiary and secondary rocks be- 

 neath, the ancient diiFerence of level is hid from our observation. Such 

 a difference, notwithstanding, remains very visible in many parts of the 

 coast of Holland, and in the north-east of Germany ; as it is also in 

 Egypt in the Natron lakes, visited by General Andreossy ; as also in the 

 bitter lakes of the isthmus of Suez, when they are left dry,^ or contain but 

 an inconsiderable depth of water. The difference of the level of the sur- 

 face of the seas, rated at five toises at the isthmus of Suez by M. Le 

 Pere, and of half a toise at the isthmus of Panama, by MM. Lloyd and 

 Palmare, are phenomena of an entirely different kind from that with 

 which we are now engaged. They are the effect of currents, of the pre- 

 ponderating direction of certain winds, of the height of the tides reflected 

 by the windings of the coasts, of the form of the canal§ by which they 

 flow or ebb, and finally, of the variations of the density of our planet. 



It is the isolated basin of the Jordan and the Dead Sea, whose hypsome- 

 tric relations have so recently engaged the attention of travellers, which 

 offers the closest analogy with the isolated basin of the Caspian Sea. The 

 determination of the boiling point of water, which, to be exact, requires 

 much care, and barometrical measurements, which, unfortunately, did 

 not accord, at first gave for the depression of the level of the Dead Sea 

 beneath the level of the Mediterranean results which varied between 500 

 and 1100 French feet (between 83 and 183 toises). The barometer of 

 M. Schubert, and the barometer of Messrs Moore and Beck, indicated 



* The mean level of lake Manetch, the enlargement of the western Manetch, 

 and consequently also of the western branch of the Kalaus, does not appear to be 

 elevated above 3 or 4 toises above the level of the Black Sea. 



t Letronne, M(m. sur Visthme de Suez, et le canal de jonction des deux mers (Rev. 

 des deux mondes, July 1841.) 



X In this state, the Bitter lakes are 20 feet beneath the level of the Mediterra- 

 nean. 



§ M. Arago, in discussing the height to which the level of water maintains itself 

 in a gulf which communicates with the ocean by a narrow canal, has pointed out 

 that it is not mathematically proved, that, by a canal of a certain form, the quan- 

 tity that enters and escapes will be the same. An accumulation of water, or a 

 rise in the level of a gulf or a narrow sea, may be produced by this cause alone.. 



