120 
Proceedings of the Royal Irish Academy. 
Parther, tlie authors of the Paper have no right to object to our 
regarding the laminated specimens as typical" Eozoon. If the 
question were as to typical ophite the case would be different ; but the 
question actually is as to certain well-defined forms which we regard 
as fossils, and allege to have organic structure on the small scale, as 
well as lamination on the large scale. We profess to account for the 
acervuline forms by the irregular growth at the surface of the organisms, 
and by the breaking of them into fragments confusedly intermingled 
in great thicknesses of limestone, just as fragments of corals occur in 
Palaeozoic limestone ; but we are under no obligation to accept irregular 
or disintegrated specimens as typical; and, when objectors reason from 
these fragments, we have a right to point to the more perfect examples. 
It would be easy to explain the loose cells of Tetradium which 
characterize the Birds-eye limestone of the Lower Siluran of America, 
as crystalline structures ; but a comparison with the unbroken masses 
of the same coral, shows their true nature. I have for some time 
made the minute structure of Palaeozoic limestones a special study, and 
have described some of them in the Trenton formation of Canada. I 
propose, shortly, to publish additional examples, showing fragments of 
various kinds of fossils preserved in these limestones, and recognizable 
only by the infiltration of their pores and other minute structures. I 
shall also be able to show that in many cases the crystallization of the 
carbonate of lime and the infiltration of other substances have 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 replace- 
ment 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 Poraminifera by hydrous silicates, as shown by 
Ehrenberg, Mantell, Carpenter, Bailey, and Pourtales.^ Parther, 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 calcareous. It is to be observed, however, that the 
wholly calcareous specimens present great difiiculties 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. 
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, &c., and 
* " Quarterly Journal Geol. Society," 1864, 
