King and Rowney— On Eozoon Canadense.'' 147 
to our descriptions and figures of the cases adduced by us to show 
that the calcite of the cell-wall of ' Eozoon' was once serpentine."'^ 
This is the true problem, that was before us ; and Dr. Hunt has not been 
able to show that our mode of solving it is any way unsound, 
i We think that Dr. Hunt has made more than was warranted of the 
I fact that both Rose and Bischof regard serpentine itself as the last 
result of the changes of a number of mineral species;" and that, 
according to the latter, it is " the very insolubility and unalterability of 
serpentine which causes it to appear as the final result." Bischof, as it 
appears to us, evidently intended his statement to be taken in a com- 
parative sense, and not to be understood as meaning that serpentine is 
absolutely insoluble and unalterable ; since he has repeatedly admitted 
that, under certain conditions, magnesian silicates are decomposed by 
carbonic acid,f and that serpentine itself may be decomposed by car- 
bonated water.J 
"With reference to the last point, silicate of magnesia is, compara- 
tively speaking, a " stable" compound; but it has been too much over- 
looked by those who regard serpentine as a final product of pseudomor- 
phism, that this mineral, besides containing a considerable percentage 
of water, is particularly prone to structural changes ; as shown by its 
frequent fibrous and flocculent allomorphs — peculiarities eminently faci- 
litating chemical substitutions : while it must not be overlooked the 
possible reaction between the calcite and serpentine, in ophite, at their 
contact surfaces, if water containing even a weak solution of carbonic 
acid penetrated into them — especially if the rock were situated at a 
great depth. 
And as regards serpentine representing the last stage of pseudo- 
morphism, we think insufficient attention has been paid to the fact that 
Bischof has qualified his view by the following remarks: — The cyclical 
character which is generally recognisable in the alteration of minerals, 
suggests the question, whether those spoken of as final products of 
alteration, may not really be particular stages of wider cycles of altera- 
tion. It is certain there is a limit to their duration. It is very probable 
that the silicates of magnesia may, under certain conditions, heconie the 
starting points of other metamorphic processes. If the silicates of mag- 
nesia were dissolved, and carried away by water, they would also take 
part in the formation of new minerals. "§ This implies the possibility 
of the removed serpentine being replaceable by another mineral sub- 
stance. Considering that chrysotile, in the condition of a vein, has 
been changed into carbonate of lime, we may safely assume that the 
displacement of serpentine, followed by a replacement in calcite, is an 
established fact. By what precise mode the change has taken place — 
* " Quarterly Journal Geol. Society," vol. xxii., pi. xiv., fig. 2, p. 192 ; " Pro- 
ceedings Eoyal Irish Academy," vol. x., pi. xli., fig. 2, p. 315. 
t "Chemical Greology," vol. i., pp. 2, 3; vol. ii., p. 123 ; vol. iii.,p. 164.. 
X lb., vol. ii., p. 434. 
§ " Chemical Geology," vol. ii., p. 113 : slightly abridged. The italicization is 
our own. 
