. Elements of geology : a text-book for colleges and for the general reader. Geology. 40 AQUEOUS AGENCIES. sity of the equatorial and polar seas would cause exchange or circulation between these regions by means of north and south currents in all longitudes, the equatorial currents being superficial because warm, and the polar currents deep-seated because cold. It is obviously impossible, however, that the principal exchange should be with the pole itself, since this is but a point, but with the northern regions. Observation shows that it is between the equator and the polar circle. In the cas
. Elements of geology : a text-book for colleges and for the general reader. Geology. 40 AQUEOUS AGENCIES. sity of the equatorial and polar seas would cause exchange or circulation between these regions by means of north and south currents in all longitudes, the equatorial currents being superficial because warm, and the polar currents deep-seated because cold. It is obviously impossible, however, that the principal exchange should be with the pole itself, since this is but a point, but with the northern regions. Observation shows that it is between the equator and the polar circle. In the case we are now considering, the exchange, being in all longitudes, would be scarcely, if at all, perceptible. Suppose, second, the earth be set a rotating: then the currents pass- ing from either polar to the equatorial region would be deflected more and more to the westward until, uniting at the equator, they would there form a directly westward equatorial current running around the earth. This westward-moving water would be constantly turning north- ward and southward in all longitudes as a superficial current, and finally eastward about the polar circle, to join again the deep-seated polar cur- rent going to the equator; thus forming a series' of regular ellipses lying over each other in strata, dipping eastward and outcropping westward—as represented in Fig. 32. As the north and south currents a a' and b V would take place in all longitudes, they would be scarcely, if at all, perceptible; but the east currents d d\ and the westward equatorial current c c, where all these unite, would be decided. In the third place, introduce continents passing across the equator from north to south, forming impassable barriers to the east and west currents c c and cl d. Then many of the lines of current a a a would be crowded against the west- ern shore of the ocean, and of the lines b b b against the eastern shore, forming in each case by concentra- tion very decided currents, while in mid
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