10 On the Physical Geology of the United States, Sc. 
to be moving northward in one of the currents of the ocean or 
atmosphere, without having lost any of its linear velocity due to 
the motion of rotation of the earth at the equator, it will, when it 
shall have arrived at 60° north latidude, still move eastward at the 
rate of twenty five thousand miles in twenty four hours, which 
would at that latitude, carry it twice* as rapidly to the eastward 
as is due to the velocity of a point on that part of the earth’s sur- 
face revolving around the axis of the earth. The resultant of 
these two forces, one tending to carry the particle to the north 
with a moderate velocity, and the other to the east with a ve- 
locity of five hundred miles per hour more rapidly than the sur- 
face of the earth moves at that latitude, would give a course 
nearly east. What is true of one particle, is true of the aggre- 
gate of particles of the currents of the atmosphere and of the 
ocean. 
- In the southern hemisphere the tendency of the currents from 
the tropics is towards the S. E., and those towards the tropics is 
to the N. W. 
The causes of the currents under consideration’ will: ‘be admit- 
ted to be permanent. 'They must, from the operation of physical 
causes, have acted through all past time since the ocean has oc- 
cupied its bed, and the earth revolved on its axis and circled 
around the sun, and they may be expected to continue to act 
through all future time. We may therefore reason upon the 
effects that may be supposed to have been produced by the action 
of these currents through long periods of past duration. 
In the Final Geological Report of New York, I have shownt 
that the contour and relative relief of the country at, and imme- 
diately preceding the drift and quaternary epochs, while most of 
the present land of the United States was beneath the level of 
the sea, was in the main the same as now, and that the land was 
elevated in mass, with little relative change of position. The 
same may be shown to have been true at preceding epochs, with 
* Let ¥ and 9" represent the distances — the axis of rotation, R the radius 
of the spies and 1 the latitude. y:9/::R:cos.l .+. Ry! = ycos./, but cos. 
60° = 4K .-. 7 = 47s o> as the cvediiirbreneen of circles are stopattiongh to 
their radii, the motion of a point on a sphere at 60° from the equator would be half 
the velocity of a point on the equator revolving around the axis of the equator. 
t Natural History of New York, Part IV, Geology of First District, by W. W. 
Mather, pp. 152-154, 629. 
