AND AMERICAN RURAL SPORTS. 
179 
diterranean ought to become as much saturated with salt as 
the brine-springs of Cheshire, or Lake Aral, or the Dead 
Sea. There is, however, an essential difference between 
these cases ; for the Mediterranean is not only incompara- 
bly greater in extent than the two last-mentioned basins, 
but its depth is enormous. In the narrowest parts of the 
Straits of Gibraltar, where they are about nine miles broad 
between the Isle of Tariffa and Alcanzar Point, the depth 
varies from one hundred and sixty to five hundred fathoms ; 
but between Gibraltar and Ceuta, Captain Smyth sounded 
to the extraordinary depth of nine hundred and fifty fath- 
oms ! where he found a gravelly bottom, with fragments of 
broken shells. Saussure sounded to the depth of two thou- 
sand feet, within a few yards of the shore, at Nice. What 
profundity, then, may we not expect some of the central 
abysses of this sea to reach ! The evaporation being, as we 
before stated, very rapid, the surface water becomes im- 
pregnated with a slight excess of salt ; and its specific gravi- 
ty being thus increased, it instantly falls to the bottom, 
while lighter water rises to the top, or that introduced by 
rivers, and by the current from the Atlantic, flows over it. 
But the heavier fluid does not merely fall to the bottom, but 
flows on till it reaches the lowest part of one of those subma- 
rine basins into which we must suppose the bottom of this 
inland sea to be divided. By the continuance of this pro- 
cess, additional supplies of brine are annually carried to 
deep repositories, until the lower strata of water are fully 
saturated, and precipitation takes place — not in thin films 
such are said to cover the alluvial marshes along the western 
shores of the Euxine, not in minute layers, like those of 
the salt “ 6tangs” of the Rhone, but on the grandest scale 
— continuous masses of pure rock-salt, extending, perhaps, 
for hundreds of miles in length, like those in the mountains 
of Poland, Hungary, Transylvania, and Spain.* 
The Straits of Gibraltar are said to become gradually 
wider by the wearing down of the cliffs on each side at 
many points ; and the current sets along the coast of Africa 
* As to the existence of an inferior current flowing westward, none of the ex- 
periments made in the late survey, give any countenance whatever to this popu- 
lar notion ; and it seems most unnecessary to resort to it, not only because the 
expenditure of the Mediterranean, by evaporation, must be immense, but because 
it is not yet proved that the two lateral currents, which conjointly exceed in 
breadth that of the centre, do not restore the equilibrium, if occasionally dis- 
turbed. They ebb and flow with the tide, but they may carry more water to the 
west than to the east. The opinion, that in the middle of the Straits the water 
returned into the Atlantic by a submarine counter-current, first originated in the 
following circumstance. M. Du l’Aigle, commander of a privateer called the 
Phoenix, of Marseilles, gave chase to a Dutch merchant ship, near Ceuta Point, 
and came up with her in the middle of the gut, between Tariffa and Tangier, 
and there gave her one broadside, which directly sunk her. A few days after, 
the sunk ship, with her cargo of brandy and oil, arose on the shore near Tan- 
gier, which is at least four leagues to the westward of the place where she sunk, 
and directly against the strength of the central current. — Phil. Trans., 1724. It 
seems obvious, that the ship, in this case, was brought back by one of the lateral 
currents, not by an under current. 
so as to cause considerable inroads in various parts, particu- 
larly near Carthage. Near the Canopic mouth of the Nile, 
at Aboukir, the coast was greatly devastated in the year 1784, 
when a small island was nearly consumed. By a series of 
similar operations, the old site of the cities of Nicopolis, 
Taposiris, Parva, and Canopus, have become a sandbank. 
LyelVs Geology. 
CESTRUS EQUI, OR THE HORSE GAD FLY. 
When the female of this species has been impregnated, 
and the eggs are sufficiently mature, she seeks among the 
horses a subject for her purpose ; and approaching it on the 
wing, she holds her body nearly upright in the air, and her 
tail, which is lengthened for the purpose, curved inwards 
and upwards : in this way she approaches the part where 
she designs to deposit her egg ; and, suspending herself for 
a few seconds before it, suddenly darts upon it, and leaves 
her egg adhering to the hair : she hardly appears to settle, 
but merely touches the hair with the egg held out on the 
projecting point of the abdomen. The egg is made to ad- 
here by means of a glutinous liquid secreted With it. She 
then leaves the horse at a small distance, and prepares a se- 
cond egg, and, poising herself before the part, deposits it 
in the same way. The liquor dries, and the egg becomes 
firmly glued to the hair : this is repeated by various flies, 
till four or five hundred eggs are sometimes placed on one 
horse. The horses, when they become used to this fly, and 
find that it does them no injury, as theTabani and Conopes, 
by sucking their blood, hardly regard it, and do not appear 
at all aware of its insidious object. The skin of the horse is 
always thrown into a tremulous motion on the touch of this 
insect, which merely arises from the very great irritability 
of the skin and cutaneous muscles at this season of the year, 
occasioned by the continual teasing of the flies, till at length 
these muscles act involuntarily on the slightest touch of any 
body whatever. 
“ The inside of the knee is the part on which these flies 
are most fond of depositing their eggs, and the next to this, 
on the side and back part of the shoulder, and, less frequent- 
ly, on the extreme ends of the mane. But it is a fact worthy 
of attention, that the fly does not place them promiscuously 
about the body, but constantly on those parts which are 
most liable to be licked with the tongue ; and the ova, there- 
fore, are always scrupulously placed within its reach. 
“ The eggs thus deposited I at first supposed were loosen- 
ed from the hairs by the moisture of the tongue, aided by 
its roughness, and were conveyed to the stomach, where 
they were hatched : but on more minute search I do not 
find this to be the case, or at least only by accident; for, when 
