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.'] 



Fig. 2. 



