INTRODUCTION. 
11 
from the earth’s rotation, which deflects it to the right, in the northern 
hemisphere, but to the left, in the southern,” 
To the obvious objection that the deflective force of the river current 
is too inconsiderable to produce such effects, the equally obvious answer 
is, that though the force be small, it has been active for a very long 
period; and moreover, it may be added, that, since these river valleys 
were doubtless scooped out mainly, (as is apparent even from the above 
section), during the Drift, or Ice Period, when the volume and 
velocity of their currents were immeasurably greater than now, 
the deflective force of these currents was far from intinitesimal in amount, 
or insensible in aggregate effect. These river valleys were excavated 
while the region was elevated more than one, (probably several) hundred 
feet above its present level, and afterwards silted up during the later ages 
of the Ice Period, when it was sunk to a depth of more than 400 feet 
lower than now, and then re-excavated as the continent rose the second 
time from the sea. At the close of the Tertiary, when the coast was ele- 
vated so as to bring this territory above the waters of the Atlantic, fhe 
surface was doubtless left comparatively level with a gentle slope seaward ; 
and the rivers, in seeking their channels by the lines of quickest descent, 
may be supposed to have divided it into belts whose drainage surfaces, 
north and south, were about equal. But as their course was over the sur- 
face of uncompacted sands, clays, &c., these currents, by the incessant 
impact of their waters upon the right bank, would gradually, but more 
and more slowly, eat their way southward. Whenever an obstacle was 
encountered in this southward movement, in the form of resisting clays, 
compacted earths or projecting rocks, the course of the river above would 
be thrown into a curve with its convexity to the south. 
It is obvious that, under similar conditions, these phenomena must he 
observable elsewhere, that is, in regions where wide level tracts of uncon- 
solidated earths have been traversed for long periods by strong river cur- 
rents, especially by the floods of Glacial and sub-Glacial times. And even 
in regions occupied by the older rocks, the effects of this force of the 
earth’s rotation may manifest itself, for example, in latitudes where the 
decomposition of the rocks more than keeps pace with the abrasive and 
transporting power of the meteoric waters. The middle region of North 
Carolina furnishes an illustration. Observant farmers who have been 
long accustomed to haul their produce to South Carolina, across the course 
of the principal streams, have asked me why they had all the worst hills 
. to ascend going to market, and only moderate acclivities returning. In 
this region the rocks are concealed by a thick covering of earth, 30 to 50 
feet and more, (resulting from their decomposition in situ) ; so that the 
