MINERALIZED WITH SILICATES. 5 59 
sembling it under the microscope. The cell-walls of the coral are 
perfectly black and opaque, and probably carbonaceous. The coral 
found thus mineralized was examined by Mr. Billings, who had no 
doubt of its nature, though uncertain as to its generic affinities. 
After careful study of it, I am disposed to refer it to the genus 
Astrocerium of Hall, and it is not distinguishable in structure from 
A. pyriforme of that author, a species very common in the Upper 
Silurian limestones of the region in which the specimen occurs. The 
genus Astrocerium is specially characteristic of the Niagara forma- 
tion; and though Edwards doubts its distinctness from Muvosites, I 
think there are constant points of difference, especially in the micro- 
scopic characters of the cell-walls, which entitle it to be separated 
from that genus. In such specimens of Astroceriwm as are well pre- 
served, the walls of the hexagonal cells seem to have been of corneous 
texture, with minute corneous spicules instead of radiating septa. 
They have pores of communication, and there are also occasional 
larger pores or tubes in the angles of the cells. The tabule are very 
thin and apparently purely calcareous. This accounts for the sin- 
gular fact, mentioned by Hall, that the cell-walls are sometimes 
entirely removed, leaving the tabule in concentric floors like those 
of Stromatopora. I think it likely that the typical species of As- 
trocertum may have been inhabited by Hydroids, and may have been 
quite remote from Favosites in their affinities. 
The formation in which the serpentine and limestone of Lake 
Chebogamong occur is described as consisting of chloritic slates, in 
some places with hornblende crystals, dolomites, and hard jaspery 
argillaceous rocks. Upon these rest conglomerates and breccias 
with Laurentian fragments, and also fragments of the rocks before 
mentioned, and on these lie the limestone and serpentine. The ser- 
pentine has been analysed by Dr. Hunt, who finds it to contain 
chromium and nickel, and in this respect to be similar to that of 
the Quebee group, and not to that of the Laurentian*. The fossil 
would give evidence of a much later date than that usually attributed 
to rocks of the character above stated; but it is quite possible that 
there may be two series of different ages in the region, the lower 
being Lower Silurian or perhaps older, and the upper of Upper Si- 
lurian age. If the serpentine belongs to the newer formation, its 
association with a coral of the genus Astroceriuwm would of course be 
quite natural. If it belongs to the older formation, and the over- 
lying limestone to the newer, the serpentine in the latter may be a 
remanté silicate derived from the older rocks and mixed with the 
limestone at their junction. 
2. Serpentine of Mclbourne.—The serpentines of this place belong 
to a great series of more or less altered rocks extending through 
the province of Quebec, and referred by Sir William Logan, on stra- 
tigraphical grounds, to his Quebec group, equivalent to the Arenig 
or Skiddaw series of England+. In ascending order these rocks at 
Melbourne present first a thick series of highly plumbaginous schists 
* Report of Geological Survey of Canada, 1870-71. 
+ Hunt, however, holds that these rocks are in part Huronian, 
