THE FOSSIL FLORA. 
201 
pally consists, being, as before stated, a crystalline compound, its con¬ 
stituents must have been in a state of solution. Cannel, or Parrot 
Coal, often bears the impression of plants, as does the third variety ; 
but it is possible to prepare slices of all of them so thin as to be 
transparent, which, upon examination by the microscope, show the 
tissue of the original vegetables very clearly ; Cannel coal seems to 
retain it throughout the whole mass, whilst it exists in fine coal in 
small patches only, which appear, as it were, mechanically entangled. 
By the microscopic examination of coal, a singular arrangement 
becomes visible ; a number of elongated tubular passages are found, 
filled with a beautiful wine-yellow coloured resinous matter, which is 
the most volatile part of the solid coal, being what is first driven off’ 
when coal is exposed to heat. Each variety of coal exhibits this 
structure in a greater or less degree, but fine coal the least, as, in it, 
the vegetable elements appear to form an almost perfect union. When 
the different varieties of coal occur together in the same seam, or bed, 
as they frequently do, they are not indiscriminately mixed, but have 
a well defined line of separation between them. In Wylam Colliery, 
near Newcastle, the principal bed of coal is, at its lower part, a fine 
splint, approaching Cannel, the middle and main part is crystalline 
coal, and the upper part of the seam is a mixture of the other two, in 
alternate layers, thus presenting, in one seam, all the three varieties 
of the Newcastle district. But it is not the seams of coal only which 
exhibit these abrupt changes of nature, as small specimens may be 
gathered at the 'mouth of every mine, which, within the compass of 
an inch, will, upon their perpendicular faces, show alternate layers of 
fine crystalline coal, and coal destitute of crystalline structure. It is 
certain each bed of coal, and more particularly each separate layer in 
that bed, musthavebeen placed in precisely similar circumstances since 
the depositon of the vegetable matter of which it is composed; and 
we cannot suppose that matter to have obtained any of its elements 
after it was buried in the earth, but rather that the difference between 
the several varieties of coal and recent vegetables, as shewn by analysis 
must have arisen from the play of affinities which has taken place in 
the mass when reduced to such a state as to allow of motion amongst 
the particles, (the result of the most complete solution of the fibre 
being tbe finest coal, whilst in the indifferent varieties this motion 
appears to have been obstructed by the tissue,) from which it seems 
naturally to follow that the several varieties of coal arise from some 
difference existing, previous to deposition, and that difference is 
most likely to have been, originally, in the nature of the plants, of 
whose remains the coal beds consist. If we are right in this con- 
