strong wind in one direction often causes the elevation
of the water, and its accumulation on the leeward side; and while the
equilibrium is restoring itself, powerful currents are occasioned. In
October, 1833, a strong current in Lake Erie, caused partly by the set
of the waters towards the outlet of the lake, and partly by the
prevailing wind, burst a passage through the extensive peninsula called
Long Point, and soon excavated a channel more than nine feet deep and
nine hundred feet wide. Its width and depth have since increased, and a
new and costly pier has been erected; for it is hoped that this event
will permanently improve the navigation of Lake Erie for
steamboats.[455] On the opposite, or southern coast of this lake, in
front of the town of Cleveland, the degradation of the cliffs had been
so rapid for several years preceding a survey made in 1837, as to
threaten many towns with demolition.[456] In the Black Sea, also,
although free from tides, we learn from Pallas that there is a
sufficiently strong current to undermine the cliffs in many parts, and
particularly in the Crimea.

_Straits of Gibraltar._--It is well known that a powerful current sets
constantly from the Atlantic into the Mediterranean, and its influence
extends along the whole southern borders of that sea, and even to the
shores of Asia Minor. Captain Smyth found, during his survey, that the
central current ran constantly at the rate of from three to six miles an
hour eastward into the Mediterranean, the body of water being three
miles and a half wide. But there are also two lateral currents--one on
the European, and one on the African side; each of them about two miles
and a half broad, and flowing at about the same rate as the central
stream. These lateral currents ebb and flow with the tide, setting
alternately into the Mediterranean and into the Atlantic. The excess of
water constantly flowing in is very great, and there is only one cause
to which this can be attributed, the loss of water in the Mediterranean
by evaporation. That the level of this sea should be considerably
depressed by this cause is quite conceivable, since we know that the
winds blowing from the shores of Africa are hot and dry; and
hygrometrical experiments recently made in Malta and other places, show
that the mean quantity of moisture in the air investing the
Mediterranean is equal only to one half of that in the atmosphere of
England. The temperature also of the great