CONTEMPORARIES OF EOZOON 1 99 



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 appear- 

 ance ; and these sometimes include grains, patches, or 

 fibres of graphite. In Cambro-Silurian limestones, 

 fragments of corals and shells which have been par- 

 tially infiltrated with bituminous matter, show a 

 structure like this. On comparison with altered 

 organic limestones of the Cambro-Silurian system, 

 these appearances would indicate that, in addition 

 to the debris of Eozoon, other calcareous structures, 

 more like those of crinoids, corals, and shells, have 

 contributed to the formation of the Laurentian lime- 

 stones. 



" (3) In the hydrous silicate (Loganite) filling the 

 chambers of a large specimen of Eozoon from 

 Burgess, there are numerous small pieces of foreign 

 matter ; and the silicate itself is laminated, indicat- 

 ing its sedimentary nature. Some of the included 

 fragments appear to be carbonaceous, others cal- 

 careous ; but no distinct organic structure can be 

 detected in them. There are, however, in the Logan- 

 ite, many minute silicious grains of a bright green 

 colour, resembling greensand concretions ; and the 



