Professor Harkness on Coal. i 
had when forming the sheath of the original plant, but it is seen in 
a-fragmentary state. This portion of the original tissue of the 
plants which compose coal, is generally found having an aspect re- 
sembling charcoal, and is, in some localities, known under the name 
of ** Mother Coal.’’ In ordinary coals, it is frequently seen in the 
form of a thin silky coating, covering some of the surfaces of the coal, 
from which it may be detached by a needle, and, when examined by 
a microscope, it affords the usual appearances presented by this por- 
tion of the vegetable tissue. In cannel coals, it is commonly seen in 
a form which has somewhat of a wedge shape, embedded in a frag- 
mentary state in the matter of the cannel itself. ‘There can be no 
doubt that, when it occurs in this state, it has been floated, and 
afterwards been embedded in the mass from whence resulted the can- 
nel. The form in which we have this in cannel, namely, as wedge- 
shaped fragments, affords us evidence of the manner in which this 
portion of the vegetable structure becomes separated from the cellu- 
lar portion, leaving the space which it occupied in the form of a hol- 
low cylinder. ‘These wedge-shaped fragments are the portions of 
the vascular cylinder, which are separated from each other by the me- 
dullary rays, and when decomposition takes place, these medullary 
rays give way, and the vascular tissue, which is arranged as a series 
of wedges round the pith, being no longer supported, floats away, if 
there be water, and these floating fragments in time become water- 
logged, and falling to the bottom become embedded in the mass of 
matter forming the coal. This mode of occurrence of the vascular 
portion of the coal is not confined to the coal seams of the true car- 
boniferous formation ; but it has been also met with, according to 
Dr Hooker, in the oolitic coal of Virginia. The manner in which 
this ‘* Mother coal” is associated with the cannels and ordinary coals 
supports the conclusion, that coal has been formed under water, 
otherwise it would be difficult to account for this substance occurring 
in -fragments embedded in the coaly mass. There is a substance 
which is nearly allied to mother coal, except that it has formed the 
vascular sheath of other forms of plants than those which enter into 
the composition of coal, and this occurs in the cale grits of the 
_ Yorkshire oolites, in a somewhat similar form, and consists of por- 
tions of the vascular system of the flora of this epoch, which, like 
the ‘‘ Mother Coal”’ of the carboniferous formation, have floated 
about ; but, in the oolite, after they had become water-logged, in- 
stead of sinking among a mass of vegetable matter, they became 
mingled with sand, and now appear as fragments of coal in sand- 
stone strata. The occurrence of fossils, in a comparatively perfect 
state, in the cannel seams, also supports the conclusion that this 
substance has been deposited under water, since we not only find 
_ plants embedded therein, but likewise the remains of fishes in 
a fragmentary state, as is the case with the Wigan cannel, which 
often contains these remains in the form of iron pyrites ; and 
