h oscillatory
changes of level, either upward or downward, are quite the rule, and
it could not be denied that these observed changes, if continued long
enough in one direction, would produce the highest elevations. The
possibility that the making of even the highest ranges of mountains had
been accomplished without exaggerated catastrophic action came to be
freely admitted.

It became clear that the supposedly stable-land surfaces are in
reality much more variable than the surface of the "shifting sea"; that
continental masses, seemingly so fixed, are really rising and falling
in billows thousands of feet in height, ages instead of moments being
consumed in the sweep between crest and hollow.

These slow oscillations of land surfaces being understood, many
geological enigmas were made clear--such as the alternation of marine
and fresh-water formations in a vertical series, which Cuvier and
Brongniart had observed near Paris; or the sandwiching of layers of
coal, of subaerial formation, between layers of subaqueous clay or
sandstone, which may be observed everywhere in the coal measures. In
particular, the extreme thickness of the sedimentary strata as a whole,
many times exceeding the depth of the deepest known sea, was for the
first time explicable when it was understood that such strata had formed
in slowly sinking ocean-beds.

All doubt as to the mode of origin of stratified rocks being thus
removed, the way was opened for a more favorable consideration of
that other Huttonian doctrine of the extremely slow denudation of land
surfaces. The enormous amount of land erosion will be patent to any
one who uses his eyes intelligently in a mountain district. It will be
evident in any region where the strata are tilted--as, for example, the
Alleghanies--that great folds of strata which must once have risen miles
in height have in many cases been worn entirely away, so that now a
valley marks the location of the former eminence. Where the strata are
level, as in the case of the mountains of Sicily, the Scotch Highlands,
and the familiar Catskills, the evidence of denudation is, if possible,
even more marked; for here it is clear that elevation and valley have
been carved by the elements out of land that rose from the sea as level
plateaus.

But that this herculean labor of land-sculpturing could have been
accomplished by the slow action of wind and frost and shower was an
idea few men could grasp within the first half-c