222 
GEOLOGY OF THE FIRST DISTRICT. 
The third cause is as permanent as the existence of the ocean, and the rotation of the earth 
on its axis. The equatorial current (which, in the Atlantic ocean, after being deflected in its 
course by the eastern coAst of South America, through the Caribbean sea and the Gulf of 
Mexico, into the North Atlantic, is called the gulf stream,) disturbs the equilibrium of the 
spheroid (the earth), rotating with its present velocity, and requires a compensating current 
from the polar regions to restore it. Another reason for a polar current, is, that the waters of 
the ocean under the equator being more heated, expand, and become specifically lighter; and 
although this cause may be scarcely appreciable, still it undoubtedly has an influence in a ten¬ 
dency to add to the equatorial current, and slightly increase its flow towards the polar regions, 
similar to the more marked effects that we know are produced by the same causes acting on 
the atmosphere. 
Mr. Redfield has shown* that the Polar or Labrador current is continued southwest along 
the coast line of the United States; and that it is not an eddy, in the usual acceptation of the 
term, but that the Gulf stream is superimposed upon and contained in this current. They 
flow in opposite directions, as we often see the clouds at different elevations, when moved by 
different currents in the atmosphere. The Labrador current brings the ice islands and drift 
ice from Davis’s strait; and “in its progress to the lower latitudes, is kept in constant proxi¬ 
mity to the American coast, by the dynamical law or influence which, in the northern hemi¬ 
sphere, caused all currents which pass in a southerly direction to incline towards the west, in 
consequence of the increasing rotative motion of the earth’s crust in the opposite direction, as 
is the case of the trade winds in the lower latitudes.”* 
The drift ice of the Northern Atlantic is always found in the western part, and js believed 
to have been rarely if ever seen east of 42° west longitude from Greenwich,! notwithstanding 
the powerful influence of the prevailing westerly winds. Tt is brought under the melting 
influence of the gulf stream in the vicinity of the Banks of Newfoundland, and is still carried 
southward by the same current which flows beneath the gulf stream, the superposition being 
determined by the relative temperatures. 
These currents (the Labrador current and the Gulf stream) are but local examples of the 
currents that act as means of compensation, tending to restore the equilibrium of the rotating 
spheroid (the earth), disturbed by the various causes mentioned, namely, the secular refrige¬ 
ration, the inertia of the ocean, and changes of temperature in the waters of the ocean. There 
may also be other causes. 
The causes that have been mentioned must have produced similar effects through all time 
since the oceans have existed, and they may be calculated on to produce similar compensating 
effects through all time to come. We may therefore reason upon the effects that may have 
been produced in times past by such causes; and in doing so, I now purpose to confine the 
reasoning to North America; not that the same train of investigation will not be applicable 
♦ Redfield. American Journal of Science, Vol. 32, p. 350. 
t Nautical Magazine, March 1837, p. 139. American Journal of Science, Vol. 32. p. 351. 
