178 
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 inhabitants, 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 reasons, for what to us appeared a great and marvel- 
lous secret.” Hutton. 
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. But there are also two lateral 
currents — one on the European, and one on the African 
side; each of them about two miles and a half broad, and 
flowing at about the 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 four 
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 velocity, 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, were found by 
Dr. Wollaston not to exceed in density 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 i 
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 
of soda can, in like manner, be precipitated, the wh 
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