'The Transactions of the Bombay Geographical Society. From December 1854 to March 1856. (New Issue.) Edited by the Secretary. Volume XII.' [‎9] (28/258)

CONTINENTAL RIVER BASINS.
IX
those at the sources of our streams will undergo the transformation into plains
and levels their predecessors along their tracks have already undergone. The
depth of many of our lakes is very great indeed, the bottom of their basins
being often far below the level of the sea ; so that were their supplies of water
diminished or the evaporation from their surfaces increased, we should have
examples presented us wherever this prevailed parallel to that with the lakes
of Asphaltites, Assal, Tiberias, the Caspian Sea, and many others, of a pool of
entirely salt water at the bottom of a hollow lower than the level of the sea ;
and to this class of hollows only do we give the name of depressions.
The bottoms of Lochness and some of the other lakes along the line of the
Caledonian canal, are not only below the level of the surface of the German
Ocean, but beneath that of its bed anywhere in the line of their axis across
to the shores of Norway.
Were the Straits of Babelmandeb closed, the Red Sea would be all but
dried up in a moderate lapse of years, presenting us with a huge chasm,
in some places half a mile in depth, with a long narrow bitter lake, margined
with rock-salt at the bottom.
The following are some of the dimensions of the most notable of our lakes ■
Names.
Area.
Elevation
of surface.
Depth.
Bottom
below Sea.
Sq. miles.
Feet.
Feet.
Feet.
Geneva
240
1,230
672
1,012
932
Superior
32,000
300
Ontario
279
12,846
—329*
547
268
Titicaca
2,225
50
720
Tiberias... ......
165
494
Dead Sea
185
—1,312
1,300
2,612
Caspian Sea
140,000
—82
82
I shall turn next to the great continental river basins, or valleys of no outlet,
where the rivers on all sides flow towards some central lake or lakes, and
the whole of their waters are carried off by evaporation. These may be
* Mrs. Somerville says in a note on tliese depressions that the level of Tiberias as given
by actual measurement of Symonds is not to be relied upon, as it falls short by above 100
feet of that determined barometrically by three dilferent observers—Berton, Russerger, and
Von Wildenbruch, who give the mean at 755—the mean assigned to the Dead Sea by the
traveller is 1423.5. With great deference to so distinguished an authority as Mrs Somerville,
I should certainly prefer the most ordinary levelling over so moderate a distance to the best
barometric measurements where there could be no good barometer of reference to fall
back upon. The hour of the day might make all this difference—the barometer read at 10
or 4 without a corresponding reading at the same level at exactly the same hour would give
an error of 100 feet.