528 



to be both gradually and abruptly changing into flocculite, cylindrical 

 rods, and aciculi. Hence, it is impossible to resist the more compre- 

 hensive conclusion that, in this case, the " canal system," " chamber 

 casts," and "nummuline layer," are all structural modifications of ser- 

 pentine. 



We may digress to bring forward another case strongly tending in the 

 same direction. Decalcified specimens, before us, of an ophite, beautifully 

 " eozoonal,"* have the chamber easts" consisting, as usual, of green ser- 

 pentine, which, however, frequently changes colour, becoming here 

 opaque white, and there colourless and translucent. The serpentine is 

 in some places, as represented in Fig. 8 (PL XLIIL), affected with two 

 dissimilar sets of cleavage, one lamellar, and the other somewhat fibrous, 

 intersecting each other obliquely (a, b.) Occasionally this phenomenon 

 first shows itself by the set, a, alone, and next by the gradual introduction 

 of the other or fibrous set, b. "Where both sets are fully developed, the 

 cleavage partings are each often wide, which causes the "chamber casts/' 

 now opaque and white, or translucent, to appear as if broken up into 

 long slender rhomboidal prisms. \ Next, the cleavage solids become 

 more and more separated from one another, their edges at the same 

 time getting more and more rounded off ; so that, at last, they appear 

 as clusters of cylindrical rods (<?), un distinguishable from the " brush- 

 like" examples of the " canal system. "| 



Clearer evidence of the conversion of the serpentine into the " de- 

 finite shapes," forming the " canal system," cannot be required ; and it 

 corresponds remarkably with the one furnished by Dr. Carpenter's 

 section ; the only difference being that in the latter the rods are generally 

 milk-white and opaque; while in the JSTeibiggen specimen they are 

 nearly colourless and translucent. This is the character generally of the 

 " canal system" in the latter specimen, whether it is represented by 

 simple or dendritic forms. 



* We got a small slab of this ophite (which, as far as can be made out, is labelled 

 Neibiggen), in London, in the summer before last. The locality appears to be in Ger- 

 many. 



t The third cleavage set, intersecting both the other sets, necessary to form a com- 

 plete solid, was not observed ; but from the peculiar obliquity of the prisms, and the 

 dissimilarity of the sets that are exhibited, we are disposed to regard these prisms as 

 triclinic (Fig. 8x represents a transverse section of one of the prisms): in this case, 

 serpentine may belong to the trebly oblique system. Dr. Carpenter's section also 

 shows the serpentine, in some places, broken up by two dissimilar sets of cleavage, ob- 

 liquely intersecting each other ; but the resulting prisms are often not so regular as 

 those occurring in the Neibiggen ophite : it is also noteworthy that the cracks which 

 cut through the adjacent layers of serpentine and calcite ("chamber casts" and "in- 

 termediate skeleton") in Dr. Carpenter's section correspond in direction with the 

 least developed set ; while the layers themselves run more or less parallel with the 

 other, or better developed set. This coincidence is curious ; and it is suggestive of the 

 possibility that there is some relation between the rude and the regular divisional structure 

 of serpentine, and the acervuline and the laminar arrangement of the " chamber cast of 

 Eozoon" respectively. 



X In the figure, only the tops of the rods are represented, as seen when looking down 

 upon them. 



