OPPONENTS AND OBJECTIONS. 195 



a special study, and have described some of them from the 

 Silurian formations of Canada.* I possess now many ad- 

 ditional examples, showing fragments of various kinds of 

 fossils preserved in these limestones, and recognisable only by 

 the infiltration of their pores with different silicious minerals. 

 It can also be shown that in many cases the crystallization 

 of the carbonate of lime, both of the fossils themselves and 

 of their matrix, has not interfered with the perfection of the 

 most minute of these structures. 



The fact that the chambers are usually filled with silicates is 

 strangely regarded by the authors as an argument 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 Forarninifera by hydrous silicates, as shown by 

 Ehrenberg, Mantell, Carpenter, Bailey, and Pourtales.f 

 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 a sedimentary limestone, and that several 

 fragmental specimens from Madoc are actually wholly cal- 

 careous. 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 col- 

 lectors in consequence of their not being developed by weather- 

 ing, or showing any obvious structure in fresh fractures. 



3. 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, etc., 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 



* In the Canadian Naturalist. 



t Quarterly Journal Geol. Society, 1864. 



