nse valleys, and their sides form elevated
crests and pass into mountain ranges.

He brings out and emphasizes the fact, now so well known, that the
erosive action of rain and rivers has formed mountains of a certain
class.

"It is then evident to me, that every mountain which is not the
result of a _volcanic irruption_ or of some local catastrophe, has
been carved out from a plain, where its mass is gradually formed,
and was a part of it; hence what in this case are the summits of
the mountains are only the remains of the former level of the plain
unless the process of washing away and other means of degradation
have not since reduced its height."

Now this will apply perfectly well to our table-lands, mesas, the
mountains of our bad-lands, even to our Catskills and to many elevations
of this nature in France and in northern Africa. But Lamarck
unfortunately does not stop here, but with the zeal of an innovator, by
no means confined to his time alone, claims that the mountain masses of
the Alps and the Andes were carved out of plains which had been raised
above the sea-level to the present heights of those mountains.

Two causes, he says, have concurred in forming these elevated plains.

"One consists in the continual accumulation of material filling the
portion of the ocean-basin from which the same seas slowly retreat;
for it does not abandon those parts of the ocean-basin which are
situated nearer and nearer to the shores that it tends to leave,
until after having filled its bottom and having gradually raised it.
It follows that the coasts which the sea is abandoning are never
made by a very deep-lying formation, however often it appears to be
such, for they are continually elevated as the result of the
perpetual balancing of the sea, which casts off from its shores all
the sediments brought down by the rivers; in such a way that the
great depths of the ocean are not near the shore from which the sea
retreats, but out in the middle of the ocean and near the opposite
shores which the sea tends to invade.

"The other cause, as we shall see, is found in the detritus of
organic bodies successively accumulated, which perpetually elevates,
although with extreme slowness, the soil of the dry portions of the
globe, and which does it all the more rapidly, as the situation of
these parts gives less play to the degradation of the surface caused
by the rivers.

"Dou