AND AMERICAN RURAL SPORTS. 



179 



dlterranean 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 oi 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 merelj^ 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 "etangs" 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 llie Mediterranean, by evaporation, must be immense, but because 

 it is not yet proved that llie 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 counler-culTent, first originated in the 

 following circumstance. M. Du I'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, wiih her cargo of brandj' 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 17S4, 

 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. 



Lyell's Geology. 



CCSTRUS 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 



