TRANSACTIONS OP THE SECTIONS. 167 



<5over extensive tracts of the steppes — or might altogether disappear by dn'ing 

 lip, as seems to have been the case with a depressed area lying between Lake 

 Elton and the River Ural, which is 79 feet below the level of the Caspian, and 

 about as much more below that of the Black Sea. It is impossible that a more 

 " pregnant instance " could be adduced of the eifect of evaporation alone in main- 

 taining a powerful current, than is afforded by this case of the Karaboghaz. 



That when the basin of the Caspian had been once completely isolated, the level 

 of its water was rapidly lowered by evaporation, until its area was so far reduced 

 as to keep down the amount of evaporation to that of the return of fresh water by 

 rain and rivers, is shown by Von Baer to be an almost inevitable inference from 

 facts of two independent orders. At the height of from 65 to 80 feet above the 

 present level, the rocks which formed the original sea-shore of the southern basin 

 have been furrowed out into tooth-shaped points and needles ; lower down, on the 

 contraiy, the rocks now laid bare show no trace of the erosive action of the water ; 

 so that its level would seem to have sunk too rapidly to allow the waves sufficient 

 time to attack the clifl-walls effectively. Again, along the shallow border of the 

 northern basin, the shore for a space of 250 miles is gashed with thousands of 

 narrow channels, from 12 to 30 miles in length, separated by chains of hUlocks, 

 which pass inland into the level ground of the steppes. In the neighbom-hood of 

 the mouths of the Volga, which brings down a greatly increased volume of water 

 at the time of the melting of the snows, the excess flows into these channels, and 

 thus tends to keep them open ; so that, when the inundation is over, the sea again 

 passes up them. Further to the south, on the other hand, the channels, like the 

 intervening hillocks, are not continuous, but form chains of little lakes separated 

 by sandy isthmuses. Although these channels run nearly parallel to each other, 

 yet they have a somewhat fan-like arrangement, their centre of radiation being 

 the higher part of the isthmus which separates the slope of the Caspian from that 

 of the N.E. portion of the Black Sea. It is difficult to see how these channels can 

 have been formed, except by the furrowing of the soft soil during the rapid 

 sinking of the level of the Caspian water, as happens on the muddy banks of a 

 reservoir in which the water is being rapidly lowered by the opening of a sluice- 

 gate. 



Now since, in the area of the Caspian as at present limited, an equilibrium has 

 been established between the qviantity of water lost by evaporation and that 

 returned to it by rain and rivers (for there is no reason to believe that any con- 

 tinuous change of level is noio going on), we can arrive at a better idea of what 

 the amount of such evaporation really is, from what is needed to make it good, 

 than we have any other means of forming. The Volga is, next to the Danube, the 

 largest European river, and its drainage-area is enormous ; the Ural is a consider- 

 able river, probably not bringing down much less water than the Don ; whilst the 

 Kur and the Araxes, which drain a large pai't of Transcaucasia, cannot together be 

 much inferior to the Dnieper ; and yet the whole mass of water brought down by 

 these four rivers serves only to keep the present level of the Caspian from being 

 further lowered by evaporation. 



On the Equa torial Lakes of Africa. By Signor Guido Coea. 



On a Portable Ghhe, and on some Maps of tlie World. By G. H. Daewin. 



On tTie Scientific Voyage of the ' Challenger.' 

 By Captain J. E. Davis, E.N., F.E.G.S. 



Captain Davis having briefly described the circumstances that led to the 

 Government imdertaking to send the ' Challenger ' on a voyage of scientific 

 discovery round the world, and also the ship herself and her fitting for the 

 voyage, which, he said, were most perfect in every particular, he proceeded : — 

 The * Challenger ' sailed from Portsmouth on the 21st of December, and on her 



