aline waters. This gave
rise to a production of sulphuretted hydrogen which is found in the
deposits, as well as in the deeper waters.

Observations in temperature and salinity have only been taken during
summer. During summer the surface salinity of the Black Sea is from 1.70
to 2.00% down to 50 fathoms, whereas in the greater depths it attains a
salinity of 2.25%. The temperature is rather remarkable, there being an
intermediate cold layer between 25 and 50 fathoms. This is due to the
sinking of the cold surface water (which in winter reaches
freezing-point) on to the top of the denser more saline water of the
greater depths. There is thus a minimum circulation in the greater
depths causing there uniformity of temperature, an absence of the
circulation of oxygen by other means than diffusion, and a protection of
the sulphuretted hydrogen from the oxidation which takes place in
homologous situations in the open ocean. The temperature down to 25
fathoms is from 78.3 deg. to 46.2 deg. F., and in the cold layer,
between 25 and 50 fathoms, is from 46.2 deg. to 43.5 deg. F., rising
again in greater depths to 48.2 deg. F.

The _Sea of Marmora_ may be looked upon as an arm of the Aegean Sea and
thus part of the Mediterranean proper. Its salinity is comparable to
that of the eastern basin of the Mediterranean, which is greater than
that of the Black Sea, viz. 4%. Similar currents exist in the Bosporus
to those of the Strait of Gibraltar. Water of less salinity flows
outwards from the Black Sea as an upper current, and water of greater
salinity from the Sea of Marmora flows into the Black Sea as an
under-current. This under-current flows towards Cape Tarhangut, where it
divides into a left and right branch. The left branch is appreciably
noticed near Odessa and the north-west corner; the right branch sweeps
past the Crimea, strikes the Caucasian shore (where it comes to the
surface running across, but not into, the south-east corner of the Black
Sea), and finally disperses flowing westwards along the northern coast
of Asia Minor between Cape Jason and Sinope. This current causes a
warmer climate where it strikes. So marked is this current that it has
to be taken into account in the navigation of the Black Sea.

The _Sea of Azov_ is exceedingly shallow, being only about 6 fathoms in
its deepest part, and it is largely influenced by the river Don. Its
water is considerably fresher than the Black Sea, varying from 1.55 to
0.68%