a LT LE ET LTE OTe AO TES 
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Wyville Thomson—General Ocean Circulation. 351 
account of the high specific gravity dependent on its low tem- 
perature, it supplies the place of the water which has been 
remo 
The cold water wells northward, but it meets with some 
obstructions on its way, and these obstructions, while the 
lstance nearer home. Evaporation is greatly in excess of 
Precipitation over the area of the Mediterranean, and conse- 
quently, in order to keep up the supply of water to the 
Mediterranean, there is a constant inward current through the 
Straits of Gibraltar from the Atlantic; I need not at present 
refer to an occasional tidal counter-current. The minimum 
temperature of the Mediterranean is about 54° F. from a depth 
vf 100 fathoms to the bottom. The temperature of 54° is 
reached in the Atlantic at the mouth of the Straits of Gibraltar 
average depth of the ocean is a little over 2,000 fathoms, and 
y 
to be usually pits in the neighborhood of voleanic islands. In 
all the ocean basins there are depressions extending over consid- 
erable areas where the depth reaches 3,000 fathoms or a little 
more, and these depressions maintain a certain parallelism with 
the axes of the neighboring continents. ; 
Within 300 or 400 miles of the shore, whether in deep or in 
shallow water, formations are being laid down, whose materials 
Am. Jour. Sc1.—Turrp ans, Vox. XVI, No. 95.—Nov., 1878. 
