to be of the same character. But there is no
reason to suppose that the trunks of trees, as well
as other foreign substances, may not be thus incrusted,
since various foreign bodies, even of artificial production,
have been so found. Professor Buckland has mentioned
a specimen of concreted limestone from St. Helena,
which contains the recent shell of a bird’s
egg;*** and M. Peron states that, in the concretional
limestone rock of the South Coast of New Holland, the
trunks of trees occur, with the vegetable structure
so distinct as to leave no doubt as to their nature.****
(Footnote. Tubular concretions of ferruginous
matter, irregularly ramifying through sand, like the
roots of trees, are described by Captain Lyon as occurring
in Africa. Lyon’s Travels Appendix page
65.)
(**Footnote. Excursions in Madeira 1825 page
139, 140; and Bull. des Sciences Naturelles volume
4 page 322.)
(***Footnote. Geological Transactions volume
5 page 479.)
(****Footnote. Peron 2 page 75.)
It so often happens that specimens sent from distant
places, by persons unpractised in geology, fail to
give the instruction which is intended, from the want
of attention to a few necessary precautions, that the
following directions may perhaps be useful to some
of those, into whose hands these pages are likely
to fall. It will be sufficient to premise, that
two of the principal objects of geological inquiry,
are, to determine, first, the nature of the MATERIALS
of which the earth is composed; and, secondly, the
relative ORDER in which these materials are disposed
with respect to each other.
1. Specimens of rocks ought not, in general,
to be taken from loose pieces, but from large masses
in their native place, or which have recently fallen
from their natural situation.
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.
