THE MEDITERRANEAN NATURALIST 
231 
Species of Western origin: 
4° Chelone rriydas (Linn.); 
5° Dermochelys coriacea (Linn.). 
Imported species: 
6’ Testudo ibera (Fallas); 
7° Testudo jnarjinatci (Schoepff). 
The Depths of the Mediterranean and 
Black Seas. (1) 
By Richard Beynon, F.R.G.S. 
Isolated as it is from the great water masses of 
the globe, the Mediterranean — with its off-set, the 
Black Sea— may be regarded as a provincial sea. 
The oceanic circulation of the North Atlantic 
sweet s past its narrow entrance unheeded. The 
great tidal wave is effectually debarred by the 
convergence of the African and European coasts 
from influencing the tidal phenomena of the Medi- 
teranean, and the same cause, aided by the near 
approach of the strata underlying the Straits of 
Gibraltar to the surface, precludes the possibility 
of the chill waters that ever roll equatorwards 
along the sea floor finding their way into the vast 
inland sea under discussion. The geographical 
limits of the Mediterranean are well known, but 
its true geological boundaries by no means coin- 
cide with these. Instead of terminating to the 
westward at the Straits of Gibraltar, the sea is 
really continued some 50 miles into the Atlantic, 
for the shoal water which separates the line of 
coast between Tangier and Ceuta from the oppo- 
site shores of Spain extends westwards to that 
distance. Here the shallow ridge terminates, and 
the sea bed rapidly falls into the depths of the 
Atlantic. 
The proximity of the island of Sicily to Cape 
Bon suggests the very natural division of the 
Mediterranean into an eastern and western section. 
Taking the western, portion, we find that at its 
two lateral extremities it is separated by a shallow 
ridge from the Atlantic on the one side, and the 
deep waters of the Eastern Mediterranean on the 
other. The depths of water obtaining on these 
shallows approximately coincide. The deepest 
sounding obtainable on the ridge between Cape 
(1) Knowledge, June 1st 1892. 
Bon and Sicily is under 200 fathoms, while the 
maximum depth in the vicinity of Gibraltar is 
180 fathoms. 
The shoal water which commences some 50 
mile's to the westward of Gibraltar is really con- 
tinued 120 miles to the eastward of Point Europa, 
almost to the shores of Alboran Island. 
If we regard as continental, islands that are 
separated from the mainland by depths not 
exceeding 100 fathoms, then Alboran must be 
classed as an oceanic island, for on all sides it is 
surrounded with water of 400 fathoms and up- 
wards in depth. The Balearic group present most 
peculiar features. Instead of forming one group, 
as their juxtaposition would seem to imply, they 
make two. Iviza and Formentara are separated from 
Majorca, Minorca, and the Spanish coast by sound- 
ings of 300 fathoms. The two last named islands 
have a channel of 50 fathoms between them, and 
to the eastwards of Minorca the sea bed has a 
steep gradient until, 30 miles from the Balearic 
group, a depth of 1400 fathoms is encountered. 
A comparatively slight upheaval of the Mediter- 
ranean bed would suffice to connect Corsica and 
Sardinia, for the- Straits of Bonifacio are of little 
depth. Shoal water, too, connects this group with 
Elba and the mainland of Italy. The shallow 
channel which extents from Cape Corso, vid Elba, 
to the coast of Tuscany has an average width of 
from 15 to 20 miles, and nowhere along it can 
soundings of a greater depth than 50 fathoms be 
obtained. 
We now come to the easterly boundary of the 
western portion of the Mediterranean Sea. 
From Cape Passaro, at the south-easterly corner 
of Sicily, a bank with 300 fathoms of water over 
it extends to the opposite shores of Tripoli, while 
a somewhat similar ridge, with a lesser depth of 
200 fathoms, connects the other extremity of the 
island with Cape Bon. Between these two banks 
a deep water gully runs, with an average depth of 
600 to 700 fathoms. 
With regard to the deep water areas of the 
western section of the Mediterranean, a fairly 
uniform depth, ranging between 1200 and 1600 
fathoms, is maintained between Marseilles and 
Algiers, while the deep water lane extending from 
Naples to Sardinia qdiqits of soundings of 1500 to 
2000 fathoms, 
