62 
utterly useless, and they will occur over a space of several 
acres, and then for the most part disappear and again occur 
as numerous as ever. For a distance of twenty-five to thirty 
miles the nodules occur in this seam of coal in more or less 
abundance, but always, so far as yet known, containing the 
same plants. Fossil shells are rarely met with in the nodules 
found in the coal, but they occur abundantly in the large 
calcareous concretions found in the roof of the mine, and are 
there associated with Dadoxylon containing Stembergia piths, 
which plant had not been noticed in the coal, and Lepido - 
strobus. So far as his experience extended, the nodules in 
the coal were always found associated with the occurrence of 
fossil shells in the roof, and were probably owing to the pre- 
sence of mineral matter held in solution in water and preci- 
pitated upon or aggregated around certain centres in the 
mass of the vegetable matter now forming coal before the 
bituminization of such vegetables took place. No doubt such 
nodules contain a fair sample of the plants of which the seams 
of coal in which they are found were formed, and their calci- 
fication was most probably in a great measure due to the 
abundance of shells afterwards accumulated in the soft mud 
now forming the shale overlying the coal. These shells, on 
their decomposition, would yield most of the minerals now 
found in the fossil wood, whilst the surrounding salt water 
and vegetables would supply the remainder. 
The specimen of Sigillaria vascularis exhibited was of an 
irregular oval shape, one foot three inches in circumference, 
had the ribs and furrows well shown on the outside of the 
decorticated stem, and afforded evidence of the structure of 
the original plant from the centre to the circumference. In 
the middle was a light coloured cylinder of about an inch in 
diameter, which appeared to be composed of carbonate of lime 
and carbonate of magnesia. The remainder of the specimen 
was of a much darker colour. By the kindness of our Presi- 
dent an analysis was made in his laboratory, by Mr. Browning, 
