ITS 



THE CABINET OF NATURAL HISTORY 



caught what we could of it in our hands, we liked it so 

 well, that we could hardly prevail with ourselves to give 

 over drinking. 



" A matter of this nature could not but incite us to make 

 the strictest observations concerning it; and, accordingly, 

 we staid under the tree about three hours, and found that 

 we could not fathom its body in five times. We observed 

 the soil where it grew to be very strong; and, upon the 

 nicest inquiry we could afterwards make, both of the na- 

 tives of the country and the Spanish inliabitants, we could 

 not learn that there was any tree of a similar nature 

 throughout New Spain, nor perhaps all America over. I 

 do not, however, relate this as a prodigy in nature; because, 

 though I am not philosopher enough to ascribe any natural 

 cause for it, the learned may perhaps be able to give sub- 

 stantial reason.s, for what to us appeared a great and marvel- 

 lous secret." Hut ion. 



PRECIPITATION OF SALT IN THE MEDITER- 

 RANEAN. 



It is well known, that a powerful current sets con- 

 stantly from the Atlantic into the Mediterranean, and its 

 influence extends along the whole southern borders of that 

 sea, and even to the shores of Asia Minor. Captain Smyth 

 found, during his survey, that the central current ran con- 

 stantly at the rate of from three to six miles an hour, east- 

 ward, into the Mediterranean, the body of water being 

 three miles and a half wide. Eut there are also two lateral 

 currents — one on tlie European, and one on the African 

 side; each of them about two miles and a half broad, and 

 flowing at about tlie same rate as the central stream. These 

 lateral currents ebb and flow with the tide, setting alter- 

 nately into the Mediterranean and into the Atlantic. The 

 escape of the great body of water, which is constantly flow- 

 ing in, has usually been accounted for by evaporation, 

 which must be very rapid and copious in the Mediterra- 

 nean; for the winds blowing from the shores of Africa are 

 hot and dry, and hygrometrical experiments recently made 

 in Malta and other places, show that the mean quan- 

 tity of moisture in the air, investing the Mediterranean, is 

 equal only to one half of that in the atmosphere of England. 

 It is, however, objected, that evaporation carries away only 

 fresh water, and that the current is continually bringing in 

 salt water: why, then do not the component parts of the 

 waters of the Mediterranean vary? or, why do they remain 

 apparently the same as those of the ocean? Some have 

 imagined that the excess of salt might be carried away by 

 an under-current, running in a contrary direction to the 

 superior; and this hypothesis appeared to receive confirma- 

 tion from a late discovery that the water taken up about 



fifty miles within the Straits, from a depth of six hundred 

 and seventy fathoms, contained a quantity of salt Jour 

 times greater than the water of the surface. Dr. Wollas- 

 ton, who analysed the water obtained by Captain Smyth, 

 truly inferred that an under-current of such denser water, 

 flowing outward, if of equal breadth and depth with the 

 current near the surface, would carry out as much salt 

 below as is brought in above, although it moved with less 

 than one-fourth part of the velocitj^, and would thus pre- 

 vent a perpetual increase of saltness in the Mediterranean 

 beyond that existing in the Atlantic. It was also remarked 

 by others, that the result would be the same, if, the swift- 

 ness being equal, the inferior current had only a fourth of 

 the volume of the superior. At the same time there 

 appeared reason to conclude that this great specific gravity 

 was only acquired by water at immense depths; for two 

 specimens of the water taken at the distance of some hun- 

 dred miles from the Straits, and at depths of four hundred, 

 and even four hundred and fifty fathoms, vv'ere found by 

 Dr. Wollaston not to exceed in densitj' that of many ordi- 

 nary samples of sea-water. Such being the case, we can 

 now prove, that the vast amount of salt brought into the 

 Mediterranean, does not pass out again by the Straits. For 

 it appears, by Captain Smyth's soundings, which Dr. Wol- 

 laston had not seen, that between the capes of Trafalgar 

 and Spartel, which are twenty-two miles apart, and where 

 the Straits are shallowest, the deepest part, which is on the 

 side of Cape Spartel is only two hundred and twenty 

 fathoms. It is, therefore, evident, that if water sinks in 

 certain parts of the Mediterranean, in consequence of the 

 increase of its specific gravity, to greater depths than two 

 hundred and twenty fathoms, it can never flow out again 

 into the Atlantic, since it must be stopped by the submarine 

 barrier which crosses the narrowest part of the Straits of 

 Gibraltar. 



What, then, becomes of the excess of salt? — for this is 

 an inquiry of the highest geological interest. The Rhone, 

 the Po, and many hundred minor streams and springs, pour 

 annually into the Mediterranean, large quantities of carbo- 

 nate of lime, together with iron, magnesia, silicia, alumina, 

 sulphur, and other mineral ingredients, in a state of chemi- 

 cal solution. To explain why the influx of this matter does 

 not alter the composition of this sea has never been thought 

 to present a great difficulty ; for it is known that calcareous 

 rocks are forming in the delta of the Rhone, in the Adriatic, 

 on the Coast of Asia Minor, and in other localities. Pre- 

 cipitation is acknowledged to be the means whereby the 

 surplus mineral matter is disposed of, after the consump- 

 tion of a certain portion in the secretions of testacea and 

 zoophytes. But some have imagined that, before muriate 

 of soda can, in like manner, be precipitated, the whole Me- 



