J. F. Campbell Collection > Short American tramp in the fall of 1864

PHYSICAL GEOGRAPHY. 13
about the foot of the Rocky Mountains, ought to be as
clear of glacial drift as the bed of the Gulf Stream in
the Atlantic now is ; but if the equatorial current passed
westwards at Panama, the old arctic current and its
drift may have reached lat. 36° 10' in these western
regions also. The memoir above quoted says (p. 19) —
' Perhaps too little consideration has hitherto been
given to the character and effects of the polar currents.
These appear to be well worthy of the attention of both
the navigator and the philosopher. We have seen that
the moderate but unceasing flow of these currents often
interposes an icy barrier in one of the most common
routes of navigation. The observing geologist will also
discern in the course of the great ice-currents of the
Atlantic, both before and after their contact with the
tropical stream, a striking coincidence with the direc-
tions of the two systems of strise which mark the
abraded surface of the continental rocks, the origin of
which must be referred to the early and prolonged
period when these rocks were situated beneath the
ceaseless flow of the ocean-currents.'*
Assuming that all North America was submerged
to a considerable depth, it seems to follow that climates
* Sillinian's Journal, vol xliii. p. 152 ; vol. xlv. p. 326.
Quoted in the memoir.