of Edinburgh, Session 1885-86. 429 
The “ Dacia ” left Cadiz on the afternoon of the 4th October. 
The entrance to the Straits of Gibraltar was reached the next 
morning, and two days were spent in thoroughly sounding its 
shallowest part, which lies nearly on a straight line connecting Cape 
Spartel on the African with Cape Trafalgar on the European coast. 
On existing published charts the bottom is seen to be very uneven. 
From Cape Trafalgar south, for more than half the distance across, 
the water does not exceed 100 fathoms in depth; then it deepens 
to 150 fathoms, suddenly shoals to 45 fathoms, then deepens again, 
and remains deep till close to the African shore. In order to assist 
in fixing the positions of the soundings, a buoy was anchored on the 
mid-channel bank. It remained down for two days. When it was 
brought on board again, the thick wire mooring-rope was found 
nearly chafed through by the violent currents rubbing it on the 
hard coral bottom. During the two days spent on this ground, a 
large number of soundings were taken, the result of which was to 
define and enlarge the mid-channel shoal from a patch a mile and a 
half long and half a mile broad to a bank 7 miles long from 
east to west by 2 miles broad from north to south ; further to 
show that the deep water runs between this bank and the African 
shore, and that the greatest depth on this, the shallowest ridge, is 
not less than 200 nor more than 210 fathoms. Considerable interest 
attaches to a knowledge of this depth. It has been supposed that 
on it depends the temperature of the deep water of the Mediter- 
ranean, as on it would depend the temperature of the coldest water 
which could find entrance into it from the Atlantic. In the 
Atlantic, however, outside the Straits, the temperature of the water 
at 200 fathoms below the surface is decidedly lower than that of the 
deep water of the Mediterranean. Moreover, it was proved by the 
observations of Sir George Hares and Dr Carpenter, in Her Majesty’s 
ship “ Shearwater,” that, though the currents in the Straits are 
affected by the tides, there is, on the whole, an inflow of Atlantic 
water at the surface and an outflow of dense Mediterranean water 
at the bottom. It was also shown b}? - M. Aime, in 1848, that the 
temperature of the deep water of this part of the Mediterranean 
agrees with the mean temperature of the coldest half of the year at 
its surface. It is probable, therefore, that the deep overflow of the 
Mediterranean has more effect in raising the temperature and density 
