provision would have then been made for conducting the rivers of the
earth; therefore, the water from the heavens, moving from the summits of
the land to the shores, must have formed for themselves those beds
or channels in which the rivers run at present; beds which have
successively changed their places over immense extents of plains that
have often been both destroyed and formed again; and beds which run
between the skirts of hills that have correspondent angles, for no other
reason but because the river has hollowed out its way between them.

In this view of things, the form of our land must be considered as
having been determined by three different causes, all of which have
operated, more or less, in producing the present state of those things
which we examine. First, There is a regular stratification of the
materials, from whence we know the original structure, shape, and
situation of the subject. Secondly, There are the operations of the
mineral region, some of which have had regular effects upon the strata,
as we find in the veins or contractions of the consolidated masses;
others have had more irregular effects, but which may still be
distinguished by means of our knowing the original state and structure
of those masses. Lastly, There are operations proper to the _surface_ of
this globe, by which the form of the habitable earth may be affected;
operations of which we understand both the causes and the effects, and,
therefore, of which we may form principles for judging of the past,
as well as of the future. Such are the operations of the fun and
atmosphere, of the wind and water, of the rivers and the tides.

It is the joint operation and result of those three different causes
that are to be perceived in the general appearances of this earth, and
not the effects of any one alone; although, in particular places of the
earth, the operation peculiar to each of these may be considered by