earth's crust, or other characters both positive and negative, such as the
presence or absence of organic remains. In the second place, the rocks of each
class may be viewed as a grand chronological series of monuments, attesting a
succession of events in the former history of the globe and its living
inhabitants.

I shall accordingly proceed to treat of each family of rocks; first, in
reference to those characters which are not chronological, and then in
particular relation to the several periods when they were formed.


CHAPTER II.

AQUEOUS ROCKS.-- THEIR COMPOSITION AND FORMS OF STRATIFICATION.

Mineral Composition of Strata.
Siliceous Rocks.
Argillaceous.
Calcareous.
Gypsum.
Forms of Stratification.
Original Horizontality.
Thinning out.
Diagonal Arrangement.
Ripple-mark.

In pursuance of the arrangement explained in the last chapter, we shall begin by
examining the aqueous or sedimentary rocks, which are for the most part
distinctly stratified, and contain fossils. We may first study them with
reference to their mineral composition, external appearance, position, mode of