accidens qui demanderaient chacun une
dissertation particuliere trop longue pour le moment, et il faut les
avoir vues pour se faire une juste idee des sentimens de grandeur, de
surprise, et d'admiration qu'elles inspirent, et que l'on ne peut pas
exprimer par des paroles. Cependant, les sources de ruisseaux, ou si
l'on veut des rivieres qui traversent ces montagnes, sont beaucoup plus
basses que les sommites des montagnes elles-memes, ces sources ne font
donc pas la cause de ces effets merveilleux. Il a fallu un agent plus
puissant pour creuser ces abimes."

M. de la Metherie has taken a very enlightened view of the country of
France; and has given us a plan of the different ridges of mountains
that may be traced in that kingdom, (Journal de Physique, Janvier 1787).
Now there is a double purpose in natural history to which such a plan as
this may be applied; viz. first, to trace the nature of the solid parts,
on which the soil for vegetation rests; and, secondly, to trace the
nature of the soil or cultivated surface of the earth, on which depends
the growth of plants.

With regard to the first, we may see here the granite raising up the
strata, and bringing them to the light, where they appear on each
side of those centrical ridges. What M. de la Metherie calls _Monts
Secondaires_, I would call the proper strata of the globe, whether
primary or secondary; and the _Monts Granit_, I would consider as
mineral masses, which truly, or in a certain sense, are secondary, as
having been made to invade, in a fluid state, the strata from below,
when they were under water; and which masses had served to raise the
country above the level of the ocean.

But this is not the subject here immediately under consideration; we are
now tracing the operations of rivers upon the surface of the earth,
in order to see in the present state of things a former state, and to
explain the apparent irregularity of the surface and confusion of the
various mineral bodies, by finding order in the works of nature; or a
general system of the globe, in which the preservation of the habitable
world is consulted.

For this last purpose also the mineral map of M. de la Metherie is
valuable. It gives us a plan of the valleys of the great rivers, and
their various branches, which, however infinitely ramified, may be
considered as forming each one great valley watered, or rather drained,
by its proper river. But the view I would now wish to take of those
v