412 
ELEMENTS OF GEOLOGY. 
same difference of durability of bark and wood exists in 
modern trees, and was first pointed out to me by Dr. Daw¬ 
son, in the forests of Nova Scotia, where the Canoe Birch 
{Betida papyracea) has such tough bark that it may some¬ 
times be seen in the swamps looking externally sound and 
fresh, although consisting simply of a hollow cylinder with 
all the wood decayed and gone. When portions of such 
trunks have become submerged in the swamps they are 
sometimes found filled with mud. One of the erect fossil 
trees of the South Joggins fifteen feet in height, occurring 
at a higher level than the main coal, has been shown by Dr. 
Dawson to have a coniferous structure, so that some Coniferce 
of the Coal period grew in the same swamps as Sigillarim^ 
just as now the deciduous Cypress (Taxodium distichum) 
abounds in the marshes of Louisiana even to the edge of the 
sea. 
When the carboniferous forests sank below high-water 
mark, a species of Spirorhis or Serpulci' (Fig. 431, p. 405), at¬ 
tached itself to the outside of the stumps and stems of the 
erect trees, adhering occasionally even to the interior of the 
bark—another proof that the process of envelopment was 
very gradual. These hollow upright trees, covered with in¬ 
numerable marine annelids,reminded me of a “cane-brake,” 
as it is commonly called, consisting of tall veedi^^Aric7idinaria 
onacrosperma^ which I saw in 1846, at the Balize, or extrem¬ 
ity of the delta of the Mississippi. Although these reeds are 
fresh-water plants, they were covered with barnacles, having 
been killed by an incursion of salt water over an extent of 
many acres, where the sea had for a season usurped a space 
previously gained from it by the river. Yet the dead reeds, 
in spite of this change, remained standing in the soft mud, 
enabling us to conceive how easily the larger Sigillarioe^ hol¬ 
low as they were but supported by strong roots, may have 
resisted an incursion of the sea. 
The high tides of the Bay of Fundy, rising more than 60 
feet, are so destructive as to undermine and sweep away con¬ 
tinually the whole face of the cliffs, and thus a new crop of 
erect fossil trees is brought into view every three or four 
years. They are known to extend over a space betAveen 
tAvo and three miles from north to south, and more than 
twice that distance from east to west, being seen in the 
banks of streams intersecting the coal-field. 
Structure of Coal. —The bituminous coal of Nova Scotia is 
similar in composition and structure to that of Great Britain, 
being chiefly derived from Sigillarioid trees mixed with leaves 
of ferns and of a Lycopodiaceous tree called Cordaites {Noeg- 
