98 SPENCER : THE AFFINITY OF DADOXYLON TO CORDAITES. 
when fragments of the bark do occur on the stems its tissues are 
generally so mineralized (changed into graphyte) that the structure 
cannot be recognized, although the woody portion of the stem may 
be in a good state of perservation. 
These fragments of Dadoxylon appear to have been drifted from 
some neighbouring land into the sea and ultimately became enclosed 
in calcareous nodules along with marine shells. It is a curious fact 
that nearly all the specimens of Dadoxylon which have been found 
and described in this country of recent years, appear to have been 
drifted fragments enclosed in similar calcareous nodules along with 
marine shells. Such fragments appear to have been met with in many 
of the marine beds throughout the Carboniferous formation. I 
have found them in the calcareous nodules of the Yoredale strata, 
Milstone Grit and Coal strata of the Parish of Halifax. They have 
been met with in similar nodules and under similar conditions in 
many other places situated on the Carboniferous formation. 
There is abundant evidence to show that most of the other 
common coal plants, such as Calamites, Lepidodendra, Sigillaria and 
ferns chiefly flourished in extensive mud flats or swamps near the 
sea level, where they formed those thick and extensive vegetable 
deposits which ultimately became converted into coal. But the 
Dadoxylons appear to have preferred the upland districts like many 
of the Coniferae of the present day. 
Storms and hurricanes appear to have periodically prevailed in 
those ancient forests, causing the uprooting of many trees and 
playing sad havoc with many others, and branches, leaves, and 
fruits, &c, were swept into the rivers and thence carried down to the 
sea, where many of them became embedded in the mud and sand at 
the rivers mouths, now composing the shales and sandstones, where 
their fossilized remains are now found, while many of the smaller 
fragments would be carried further out to sea, and becoming water- 
logged would sink to the bottom and become enveloped in those 
calcareous nodules in which they are now met with. The great 
majority of the drifted trunks and fragments would utterly perish, 
while a few only, here and there, would meet with conditions favour- 
able to their preservation in a fossil state. In some beds of stone, 
