File:The Quarterly journal of the Geological Society of London (12645098543).jpg

1848..
HALL ON ORTHOCERAS.
109
These for the most part I have destroyed to procure the enclosed
fossil, and have no good representatives from this period.
In the Hamilton group such apj)earances are quite
common, and excite little attention. The accompanying
figure (fig. 1) represents a Chemnitzia (Loxonema) with a
concretion or sac on either side, which appears as if it
may once have been a soft or pulpy mass. In another
specimen the shell is nearly covered by this sac, which
still preserves its proportions, corresponding to the form
of the shell.
In this case there could have been no external animal or soft body
to become fossilized ; and had the entire soft part of the animal been
protruded from the shell, it would not have been half so large as the
attached concretion or sac, nor would it have assumed this position.
It is evident nevertheless that the form and size of the shell, or of
the animal within it, has determined the form and proportions of the
adhering concretionary mass ; and if it could so act in this instance,
why may it not have done the same in the case of the Orthoceras ?
I am unwilling, at least, to admit the existence of such a preservation
of the "soft parts" of a Cephalopod, while we have an example so
similar among the Gasteropods. I regret that I have no other spe-
cimens at hand to show that these are far from being solitar.^ ex-
amples.
Among numerous specimens of Orthocerata, I select the accompa-
nying figures 3 and 4, which present some analogy with the figure
of Mr. Anthony*.
liar appearance of the " slickensides," except that the striae are finer. Such ac-
tion takes place almost universally in our black carbonaceous shales of all ages in
the palaeozoic period ; not only appearing in such concretionary masses enclosing
fossils of all classes, and in distinct concretions, but also marking the plane shaly
or slaty cleavages where there is no evidence of metamorphic action, and where the
strata are in nearly a horizontal position. In all these cases iron pyrites, or some
action dependent on its presence or production, seems to perform an important
part, even to the formation of pseudo-organic forms.

• .As these figures by Mr. Hall closely resemble that given in a former number
  

of the Journal, from Mr. Anthony's specimen, and here repeated, fig. 2, it has not
seemed necessary to engrave them. Mr. Hall also sent a drawing of the second
specimen of Chemnitzia mentioned above, which has likewise been omitted. — Ed.
Quart. Geol. Journ.'.