200 
PROGRESS OF MICROSCOPICAL SCIENCE. 
against the organic nature of Eozoon. One would think that the 
extreme frequency of silicious fillings of the cavities of fossils, and 
even of silicious replacement of their tissues, should have prevented 
the use of such an argument, without taking into account the opposite 
conclusions to be drawn from the various kinds of silicates found in 
the specimens, and from the modern filling of Foraminifera by 
hydrous silicates, as shown by Ehrenberg, Mantell, Carpenter, Bailey, 
and Pourtales.* Further, I have elsewhere shown that the loganite 
is proved by its texture to have been a fragmental substance, or at 
least filled with loose debris; that the Tudor specimens have the 
cavities filled with sedimentary limestone, and that several fragmental 
specimens from Madoc are actually wholly calcareous. It is to be 
observed, however, that the wholly calcareous specimens present 
great difficulties to an observer ; and I have no doubt that they are 
usually overlooked by collectors in consequence of their not being 
developed by weathering, or showing any obvious structure in fresh 
fractures. With regard to the canal system, the authors persist in 
confusing the casts of it which occur in serpentine with ‘ metaxite ’ 
concretions, and in likening them to dendritic crystallizations of 
silver, &c., and coralloidal forms of carbonate of lime. In answer to 
this, I think it quite sufficient to say that I fail to perceive the 
resemblance as other than very imperfect, imitative. I may add that 
the case is one of the occurrence of a canal structure in forms which 
on other grounds appear to be organic, while the concretionary forms 
referred to are produced under diverse conditions, none of them 
similar to those of which evidence appears in the specimens of 
Eozoon. With the singular theory of pseudomorphism, by means of 
which the authors now supplement their previous objections, I leave 
Dr. Hunt to deal. With regard to the proper wall and its minute 
tribulation, the essential error of the authors consists in confounding 
it with fibrous and acicular crystals, and in maintaining that because 
the tubuli are sometimes apparently confused and confluent they must 
be inorganic. With regard to the first of these positions, I may 
repeat what I have stated in former papers — that the true cell-wall 
presents minute cylindrical processes traversing carbonate of lime, 
and usually nearly parallel to each other, and often slightly bulbose 
at the extremity. Fibrous serpentine, on the other hand, appears as 
angular crystals, closely packed together, while the numerous spicular 
crystals of silicious minerals which often appear in metamorphic 
limestones, and may be developed by decalcification, appear as sharp 
angular needles usually radiating from centres or irregularly disposed. 
Plate 44, Fig. 10,1 is an eminent example of this ; and whatever the 
nature of the crystals may be, they have no appearance in the plate of 
being tubuli of Eozoon. I have very often shown microscopists and 
geologists the cell-wall along with veins of chrysotile and coatings of 
acicular crystals occurring in the same or similar limestones, and 
they have never failed at once to recognize the difference, especially 
under high powers. I do not deny that the tubulation is often 
* 1 Quart. Journ. Geol. Soc.,’ 18G4. 
t Ophite from Skye, King and Rowney’s paper, ‘ Proc. R. I. A.,’ vol. x. 
