. III. DIST. CHAR/ Mode. 65 



of this kind, particularly those of coral, are fre- 

 quently invested with very thin coverings of clialkij 

 matter; into which the original substance appears 

 to have passed,, while acquiring the sparry frac- 

 ture. The remains offish, as their bones, teeth, &c. 

 have sometimes, also, been subjected to a sparry 

 transmutation ; but these are almost always found 

 only partially changed: certain parts of them, (par- 

 ticularly the exterior parts ) still retaining their ori- 

 ginal substance and conformation. 



The bituminous transmutations, furnished by the 

 the animal kingdom, are, as already noticed, very- 



preserve their animal, in conjunction with their mineral texture, 

 (v. Illustrations, p. 191.) If, by the animal texture, is here meant 

 that peculiar grain, or disposition of the particles, which a recent 

 shell exhibits on being broken, we must observe, that we have 

 never yet seen this, in any calcareous petrifaction, really possess- 

 ing the sparry or rhombic fracture nor do we conceive it possible, 

 that the fracture of spar and the grain of the original matter 

 can exist together. We suppose, however, by the animal 

 texture, Professor Playfair merely intends to distinguish that stra- 

 tified or tunicated conformation, which certain bivalves possess, 

 and which is frequently evident in them, after they have undergone 

 the mineral change now referred to. This retention of the gene- 

 ral structure of the original, is easily accounted for, by the suppo- 

 sition, that each layer or stratum has separately passed through the 

 sparry transmutation; and of course, that each has preserved its 

 form distinct, in some respect, from that of the other coats of the 

 shell, to which it is attached. The same remark is also applicable 

 to the petrified remains of the entrochi aud other jointed zoophytes, 

 which, though changed into spar, still retain the internal, 

 lated structure of their stems. 



