CONTEMPORAEIES AND SUCCESSORS OF EOZOON. 131 



constitute the greater part of tlie mass. In others 

 they are embedded in calcareous matter of a different 

 character^ or in serpentine or granular pyroxene. In 

 most of the specimens the cells of the fossils are more 

 or less filled with these minerals; and in some in- 

 stances it would appear that the calcareous matter of 

 fragments of Eozoon has been in part replaced by ser- 

 pentine.^^ 



" 2. Intermixed with the fragments of Eozoon above 

 referred to, are other calcareous matters apparently 

 fragmentary. They are of various angular and 

 rounded forms, and present several kinds of structure. 

 The most frequent of these is a strong lamination 

 varying in direction according to the position of the 

 fragments, but corresponding, as far as can be ascer- 

 tained, with the diagonal of the rhombohedral cleavage. 

 This structure, though crystalline, is highly character- 

 istic of crinoidal remains when preserved in altered 

 limestones. The more dense parts of Eozoon, destitute 

 of tubuli, also sometimes show this structure, though 

 less distinctly. Other fragments are compact and 

 structureless, or show only a fine granular appearance ; 

 and these sometimes include grains, patches, or fibres 

 of graphite. In Silurian limestones, fragments of 

 corals and shells which have been partially infiltrated 

 with bituminous matter, show a structure like this. 

 On comparison with altered organic limestones of the 

 Silurian system, these appearances would indicate that 

 in addition to the debris of Eozoon, other calcareous 

 structures, more like those of crinoids, corals, and 



