(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.