Thus, in Sketch 4, which may be supposed to represent a cliff of considerable height, the observer being situated at a, the beds b, c, d, though inaccessible at that place, may be examined with ease and security, where they successively come down to the shore, at b prime, c prime, and d prime.
6.

To examine the interior of an unknown country, more skill and practice are required: the rocks being generally concealed by the soil, accumulations of sand, gravel, etc., and by the vegetation of the surface.

But the strata are commonly disclosed in the sides of ravines, in the beds of rivers and mountain-streams; and these, especially where they cross the direction of the strata, and be made, by careful examination, to afford instructive sections.
7.

Among the distinctive circumstances of the strata, the remains of organized bodies, shells, corals, and other zoophytes, the bones and teeth of animals, fossil wood, and the impressions of vegetable stems, roots, or leaves, etc., are of the greatest importance; affording generally the most marked characters of the strata in which they occur.
These should, therefore, be particularly sought after, and their relative abundance or rarity in different situations noticed.

The petrified bodies should, if possible, be kept united with portions of the rock or matrix in which they are found; and where they are numerous, in sand, clay, or any moist or friable matrix, it is in general better to retain a large portion of the whole mass, to be examined afterwards, than to attempt their separation at the time of collecting.
8.