: 
On Specimens of Eozo0on Canadense. 225 
specimen) is a limestone with perfectly regular and uniform 
layers of minute rhombohedral crystals of dolomite. The 
layers vary in distance regularly in the thickness of the 
specimen from two millimetres to one, and must have resulted 
from the alternate deposition in a very regular manner of 
dolomite and limestone. These are but a few of the examples 
of imitative structures which might readily be confounded 
with Hozoon, or which, if resulting from organic growth, 
have lost all decisive evidence of the fact. 
Perhaps still more puzzling imitative forms are those 
referred to by Hahn, which occur in some felspars, and 
which I have found in great beauty in certain crystals of 
orthoclase from Vermont. They are ramifying tubes 
resembling the canal-system of Hozoon, and are evidently a 
peculiar form of gas-cavities or inclusions. Similar appear- 
ances are, however, often presented by the more minute 
‘and microscopic varieties of graphic granite, in which the 
little plates might readily be mistaken, in certain sections, 
for organic tubulation. 
In the present state of knowledge, it is perhaps more 
excusable to mistake such things for organic structures than 
to deny the existence of true organic structures because 
they resemble such forms. Those who have examined 
moss-agates are familiar with the fact that while some show 
merely crystals of peroxide of iron or oxide of manganese, 
others present the forms of Vaucheric or Conferve. So if 
one were to place side by side some fibres of asbestos, 
spicules of Yethea, and coniferous wood, preserved, like 
some from Colorado, as separate white siliceous fibres, they 
might appear alike; but, even if thoroughly mixed together, 
the microscope should be able easily to distinguish them. 
| have specimens of fossil wood, collected by Hartt in Brazil, 
which have been mineralized by limonite in such a manner 
that no one, without microscopic examination, could believe 
them to be other than fibrous brown hematite. Such 
difficulties the micro-geologist must expect to find, and by 
patient observation to overcome, 
