CONCLUDING REMARKS. 43 
filled with substances analogous to those of which the strata containing 
them are composed. ; 
Silicified fossils occur more abundantly in the superior formations, and 
are generally of a lighter colour. The calcedonic monocotyledonous and di- 
cotyledonous fossils of the West Indies vary in colour from yellowish-white 
to reddish-brown, or even bright ‘red, but seldom or never assume tints so 
dark as those of our inferior deposits. 
With respect to the fossil vegetables of which I have presented figures, 
I may here again remark, that, notwithstanding the want of well-defined 
concentric layers in those of the coal-formation and mountain limestone 
group, no doubt remains with me as to their being Conifere. Should it be 
shewn, by future investigations, that recent plants of other classes present 
a similarity of structure, the case will become different; but until then, it 
will remain established that these fossil plants come nearer to the structure 
of the Conifer than to that of any other tribe. As to the fossils of the 
lias, I presume no doubt can henceforth remain in the mind of any one who 
may compare them with recent Conifer, or be satisfied with the accuracy 
of my representations. 
It may be well, in this place, briefly to recapitulate my observations, and 
mark out those fossil plants which I am inclined to consider as distinct spe- 
cies : 
1. The fossil vegetable from Lennel Braes, on the Tweed, represented in 
Plates IT. and III., and by Figs. 7, and 8, of Plate VI., belongs to 
the mountain limestone group. 
2. That from Craigleith Quarry, near Edinburgh, represented by the 
lower figures of Plate III., belongs either to the mountain limestone 
group or to the coal-formation. 
3. The Wideopen tree, represented by Figs. 1, 2, 3, and 4, of Plate IV., 
and by Fig. 3. of Plate VI., is of the coal-formation. The High 
Heworth tree, represented by Figs. 7, and 8, of Plate IV., which is 
from the same stratum as the Wideopen tree, is probably of the same 
species. 
F2 
