the mediterranean naturalist 
261 
The paucity of animal life in the great depths 
of the Mediterranean is well known. Its depths 
are to a certain extent stagnant. There is an 
utter absence of that vertical circulation so 
thoroughly developed in the Atlantic, and which 
results in process of time in every particle of 
water being alternately transposed from sea bed 
to surface, and surface to sea floor. The only 
semblance of such a circulation that exists in 
the Mediterranean is caused by the descent of 
water that has been concentrated by evapora- 
tion on the surface, and has thus had its specific 
gravity raised above that of the underlying strata. 
But the descent of this water will be seriously 
interfered with at a depth of 200 or 300 fathoms, 
where the temperature is such that it will en- 
counter an aqueous layer whose specific gravity is 
much akin to its own. 
It will be remembered that it was owing to the 
absence of life met rvith during the researches of 
Professor E. Forbes in the yEgean Sea, that the 
erroneous doctrine was formulated that marine 
oceanic life ceased at a depth of about 300 fathoms. 
Subsequent explorations in the deep sea speedily 
showed the fallacious character of such a con- 
clusion. except in enclosed seas of the Mediter- 
ranean type. 
In the western basin of the Mediterranean, the 
bottom consists chiefly of clay, of a grey or 
brownish colour It always contains some carbo- 
nate of lime, the remains of foraminifera. Both 
in appearance' and chemical constitution the mud 
resembles that dredged up in the open ocean from 
areas which are shut off by submarine ridges 
from free participation in the vertical oceanic 
circulation. 
In the eastern section of the Mediterranean the 
sea bed deposits contain a considerable propor- 
tion of volcanic ash and other constituents of 
igneous origin. 
Before proceeding to discuss the character of 
the connecting channels and currents that unite 
t lie Mediterranean Sea with the Atlantic Ocean 
and the Black Sea, we will briefly allude to the 
findings of the latest researches conducted in the 
waters of the last named sea. 
The Russian gun-boat the Tchernomoretz was 
engaged in June and July, 1890, in the work of 
surveying. The maximum depth, 7365 feet, was 
found in the central portion of the sea, between 
the Crimea and Anatolia The explorations were 
continued last year, and the results of the previous 
year’s work were confirmed. The 100 fathom line 
was found to lie close to the shores of the 
Crimea and Anatolia, and the axis of greatest 
depression has a direction from south-west to 
north-east. The steepest coast was found at Rizo, 
where the angle of inclination attains 10'. The 
most interesting of the recorded observations are 
those relating to the temperature of the Black Sea 
waters. The variations of temperature at the 
surface range from 77° F., to 41 F., while on the 
northern shores the thermometer sometimes falls 
below the freezing point. The annual variations 
of the temperature, due to the seasons, do not 
penetrate deeper than 100 fathoms. At a depth 
of from 30 to 175 feet the temperature was 57° 
towards the south coast, 54° in the centres, and 52° 
near the east, west, and north shores. 
The water begins to be warmed by the air in 
the month of May, and during August the mean 
temperature of the surface water is higher than 
that of the superincumbent air. The variation 
of temperature for depths below 180 feet is very 
peculiar. At this point the thermometer registers 
45° F. Then the thermometer begins to rise, 
and at a depth of 6000 feet it shows 49° F. 
For all depths below 200 fathoms the temperature 
may be described as constant, and lying between 
49 c F. and 48° F. The most distinctive feature 
of the Black Sea, however, is that at the depth 
of 450 feet distinct traces of sulphuretted hy- 
drogen occur. The quantity increases with the 
depth, until at 600 feet it is quite sensible, and 
at the mean depth of 940 feet it renders animal 
life quite impossible. Some even place the in- 
ferior limit of organic life at so high a level as 
100 fathoms. Dredging shows that at one period 
of geological history the Black Sea contained an 
abundance of low organisms, and the semi-fossil 
shells of certain molluscs characteristic of the 
brackish water of the lagoons of the Caspian and 
Black Seas are much en evidence. These fossils are 
doubtless the remains of the Pontic fauna of the 
Pliocene period when the Black Sea basin was 
not connected with the Mediterranean. The sa- 
linity of the Black Sea was then by no means so 
great as it is now. When the connection between 
