d fifty feet above the sea, at Bald-head, on the
South Coast of Australia. These specimens, however, do not really exhibit
any traces of organic structure; and so nearly resemble the irregular
stalactitical concretions produced by the passage of calcareous or
ferruginous solutions through sand* that they are probably of the same
origin; indeed the central cavity of the stalactite still remains open in
some of the specimens of this kind from Sweer's Island in the Gulf of
Carpentaria. The specimens from Madeira, presented to the Geological
Society by Mr. Bowdich, and described in his notes on that island,**
appear upon examination 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.)

INSTRUCTIONS FOR COLLECTING GEOLOGICAL SPECIMENS.

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 situatio