210 Canadian Record of Science. 
occur in such a way that similar spaces are occupied in one 
part of the fossil with one mineral, in others with another. 
In connection with this, the imperfections in the preser- 
vation of Hozoon are also parallel with those observed 
Fig. 6. Cross section of canals, injected with serpentine, highly magnified. 
in different organic substances. As an example, I have 
already mentioned that in some of the specimens a white 
flocculent serpentine encroaches upon the calcareous walls 
or in part replaces them. This would indicate the partial 
removal of the calcite prior to or at the same time with the 
filling. In some cases also the calcite wall is wholly or in 
part replaced with dolomite. Such changes are not infre- 
quent in Paleozoic fossils in which the substance of a cal- 
careous part has often been wholly removed and replaced 
by another mineral or has been partially eroded and so in 
part replaced. 
Fig. 7. Longitudinal section of canals, highly magnified. 
There are other peculiarities deserving special notice :— 
