320 THE CANADIAN NATURALIST. [Jan. 



Canada abundance of Laurentian limestone which shows no indi- 

 cation of the structures of Eozoon. In some cases it is evident 

 that such structures have not been present. In other cases they 

 may have been obliterated by processes of crystallization. As in 

 the case of other fossils, it is only in certain beds, and in certain 

 parts of those beds, that well-characterized specimens can be 

 found. I may also repeat here that in the original examination 

 of Eozoon, in the spring of 1864, I was furnished by Sir W. E. 

 Logan with specimens of all these limestones, and also with 

 serpentine-limestones of Silurian age, and that, while all possible 

 care was taken to compare these with the specimens of Eozoon, it 

 was not thought necessary to publish notices of the crystalline and 

 concretionary forms observed, many of which were very curious 

 and might afford materials for other papers of the nature of that 

 criticised in the above remarks. 



[The examination of a large number of sections of a specimen 

 of Eozoon, recently placed in my hands by Sir William Logan, in 

 which the canal-system is extraordinarily well preserved, enables 

 me to supply a most unexpected confirmation of Dr. Dawson's 

 statements in regard to the occurrence of dendritic and other 

 forms of this system, which cannot be accounted for by the intru- 

 sion of any foreign mineral ; for many parts of the calcareous 

 lamellae in these sections, which, when viewed by ordinary trans- 

 mitted light, appear quite homogeneous and structureless, are 

 found, when the light is reduced by Collin's ' graduating 

 diaphragm,' to exhibit a most beautiful development of various 

 forms of canal-system (often resembling those of Dr. Dawson's 

 Madoc specimen represented in PI. III. figs. 4, 5), which cross the 

 cleavage-planes of the shell-substance in every direction. Now 

 these parts, when subjected to decalcification, show no trace of 

 canal-system ; so that it is obvious, both from their optical and 

 from their chemical reactions, that the substance filling the canals 

 must have been carbonate of lime, which has thus completely 

 solidified the shell layer, having been deposited in the canals 

 previously excavated in its interior, just as crystalline carbonate 

 of lime fills up the reticular spaces of the skeleton of Echinoder- 

 mata fossilized in a calcareous matrix. This fact affords con- 

 clusive evidence of organic structure, since no conceivable process 

 of crystallization could give origin to dendritic extensions of 

 carbonate of lime disposed on exactly the same crystalline system 

 with the calcite which includes it, the two substances being 



