n.

2. The specimens should consist of the stone unchanged by exposure to the
elements, which sometimes alter the characters to a considerable distance
from the surface. Petrifactions, however, are often best distinguishable
in masses somewhat decomposed; and are thus even rendered visible, in
many cases, where no trace of any organized body can be discerned in the
recent fracture.

3. The specimens ought not to be too small. A convenient size is about
three inches square, and about three-quarters of an inch, or less, in
thickness.

4. It seldom happens that large masses, even of the same kind of rock,
are uniform throughout any considerable space; so that the general
character is collected, by geologists who examine rocks in their native
places, from the average of an extensive surface: a collection ought
therefore to furnish specimens of the most characteristic varieties; and
THE MOST SPLENDID SPECIMENS ARE, IN GENERAL, NOT THE MOST INSTRUCTIVE.
Where several specimens are taken in the same place, a series of numbers
should be added to the note of their locality.

5. One of the most advantageous situations for obtaining specimens, and
examining the relations of rocks, is in the sections afforded by cliffs
on the seashore; especially after recent falls of large masses. It
commonly happens that the beds thus exposed are more or less inclined;
and in this case, if any of them be inaccessible at a particular point,
the decline of the strata will frequently enable the collector to supply
himself with the specimens he wishes for, within a short distance. 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, th