66 J. WwW. DAWSON ON PALAOZOIC FOSSILS MINERALIZED WITH SILICATES. 
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 ap- 
pearances are, however, often presented by the more minute and mi- 
croscopic 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 exist- 
ence 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 Vaucheriew or Conferve. 
So if one were to place side by side some fibres of asbestos, spicules 
of T'ethea, 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. I 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. 
EXPLANATION OF THE PLATES. 
Puate ITT. 
Fig. 1. Vertical section of Stromatopora from the Niagara formation, showing 
the lamine and pillars, without supplemental matter, x 20. 
. Vertical section of Stromatopora from the Corniferous Limestone, 
showing pillars ramifying and thickened at the ends, and laminz 
without supplemental matter, x 20. 
3. Vertical section of Stromatopora from the Corniferous Limestone, with 
much supplemental matter, but showing unthickened lamine at aa, 
also horizontal canals at 6 b, x 20. 
Puate IV. 
Fig. 4. Vertical section of Stromatopora from the Corniferous Limestone, xX 2, 
showing lines of growth, aa; c, vertical section of part of the same, 
x 20; d, surface of lamina, X 20, showing solid and hollow pillars. 
5. Portion of lamina of another specimen, x 20, showing large pores and. 
bases of two pillars. 
6. Portion of another specimen, x 20, showing hollow and solid pillars 
and a pore at a. 
7. Portion of silicified Stromatopora, weathered, and showing lamine 
8 
9 
2 
and pillars in relief, x 20. 
. Portion of Stromatopora resting on a tabulate coral and showing acer- 
vuline cells at base, x 2. 
. Vertical section of Cawnopora hudsonica, showing vertical tube and 
horizontal canals, x 20; a, horizontal section of part of the same, 
showing canals and canaliculi; 4, vertical section, more magnified, 
Puater VY. 
Fig. 10. Horizontal section of Caunopora hudsonica, showing canals radiating 
from a central tube, « 20. 
11. Vertical section of Cenostroma nodulata, Corniferous Limestone, show- 
ing canals and concentric lamine, with much supplemental matter, 
x 20. 
12. Horizontal section of the same, showing large radiating canals, x 20. 
