48 J. W. DAWSON ON THE MICROSCOPIC 
3. On the Microscopic Srructure of Stromatoporipa, and on 
Patmozorc Fosstts mineralized with Siuicates, in illustration 
of Eozoon. By J. W. Dawson, LL.D., F.R.S., F.G.S8., &c. 
(Read June 5, 1878 *.) 
[Puates III.-V.] 
Amone the collateral subjects which have arisen in the discussions 
with respect to Hozoon canadense, two of the most important 
are :—Ist, the question of its structural relations with the Palaeozoic 
fossils of the genus Stromatopora and allied genera; 2nd, the oc- 
currence in Paleozoic rocks of fossils mineralized with hydrous 
silicates akin to the serpentine and loganite found in some of the 
best-preserved specimens of the Laurentian fossil. For several 
years I have taken advantage of every opportunity to make collec- 
tions illustrative of these questions, and to subject the specimens 
obtained to microscopic examination. In this I have been greatly 
aided by friends who will be mentioned in the sequel, and by the 
large number of excellent sections prepared by Mr. Weston, of the 
Geological Survey of Canada, for the late Sir W. E. Logan and for 
myself. In the following paper I purpose to state the conclusions 
arrived at as the result of these observations, with such portions as 
may be necessary of the large accumulations of facts on which they 
are based. 
I, SrromATOPoRIDz. 
1st. Microscopic Structwre-—The Stromatoporide have long been 
a zoological stumbling-block, and have been referred to Corals, 
Sponges, Foraminifera, and even to Hydractiniz. I do not purpose 
to review these diverse opinions, most of which are undoubtedly 
based on imperfect acquaintance with the microscopic structure of 
these curious fossils, but to give an intelligible account of the struc- 
ture of some typical species, preparatory to the consideration of their 
relation with Hozoon. 
The genus Stromatopora, properly so called, is founded on the 
species Stromatopora concentrica, Goldfuss, and its allies, which range 
from the Upper Cambrian to the Devonian inclusive. Avoiding, for 
the present, complexities arising from the various states of preserya- 
tion and of weathering, I may refer in the first instance to remark- 
ably well-preserved specimens from the Corniferous Limestone of 
Ohio, and from the island of Marblehead in its vicinity, which have 
been placed in my hands by Mr. A. K. Walker of Hamilton, and Dr. 
Newberry of New York. In these the concentric lamine and pillars 
of the fossil are in the condition of opaque calcite, apparently re- 
taining its minute structure and not affected by crystallization ; and 
the interspaces or chambers are occupied by transparent calcite, 
* For the Discussion on this paper sze p. 68. 
