On Specimens of Eozoon Canadense. 207 
as Eozoon is in the Laurentian limestone. These fossils are 
silicified and vary in diameter from a foot to an inch. The 
greater part are spheroidal in form, but some are cylindrical 
or club-shaped, while others spread into flat sheets or are of 
various irregular shapes. In many specimens, the structure 
is beautifully preserved; but in others it has partially dis- 
appeared, and the substance of the fossil is replaced by 
coarsely crystalline calcite or dolomite, or presents cavities 
lined with crystals of these minerals. There is reason to 
believe that many cavities in the limestone, now empty and 
coated with these crystals, were once occupied by Stro- 
matopor, or by the species of sponge found in this lime- 
stone. In every respect, except in the absence of hydrous 
silicates, the mode of occurrence of these fossils resembles 
that of Eozoon at Cote St. Pierre. 
In some such cases of replacement it is probable that the 
original material of the fossil was arragonite, and for this 
reason more easily removed or replaced. Hvery Paleonto- 
logist is familiar with the fact that arragonite or prismatic 
shell has been removed in cases where lamellar shell has 
remained, and the latter has sometimes disappeared when 
compact calcite shells, like those of Balanus, for example, 
have escaped. In the case of Kozoon, however, as in that 
of foraminifera in general, the calcite seems to have been 
of the less perishable kind, and this may be connected with 
the integrity of the calcareous wall in the better preserved 
specimens.* 
By what appears to a paleontologist a strange perversion 
of reasoning, some of the opponents of the organic nature 
of Kozoon take the badly preserved specimens as typical, 
and suppose that these represent an original mineral condi- 
tion, which in the better preserved specimens has only 
assumed its greatest perfection. 
As I have often urged, this kind of argument would 
invalidate all reasoning from the structures of fossils, In 
all large masses of fossil coral or wood, we find portions in 
* | have elsewhere remarked that the caleareous wall of Hozoon retains a finely 
granular texture, similar to thatseen in shells, etc., in altered Palssozoic limestones. 
