488 
find their interior entirely filled with indurated clay or sand, since 
it appears from effects now proceeding in tropical climates, that the 
entire bark may have retained its place and form and have been filled 
with sand or silt after the interior of the trees had rapidly perished. 
Similar observations as to the rapid decay of timber have been made 
by Mr. Schomburgh. 
Mr. J. E. Bowman also has endeavoured to prove that coal has 
_been formed from plants which grew on the present areas of the 
coal seams, and that these beds of vegetable matter were at suc- 
cessive intervals submerged, and covered by sediments, which ac- 
cumulated until they formed a surface fit for the growth of an- 
other series of land plants; and that these processes were repeated 
in the production of each bed of coal. In this manner he would 
explain the uniformity in thickness of individual coal. beds over 
very large areas. He further admits, that other trees, branches, 
and leaves, may have been drifted from the neighbouring lands, and 
scattered through the beds of shale and sandstone, whilst they were 
in process of accumulation upon the subsiding or subsided beds of 
coal. Mr. Bowman agrees with Mr. Hawkshaw in believing the 
large trees upon the Bolton Railway, near Manchester, to be in their 
native place and position, and to have been dicotyledonous. He 
further mentions a similar case of at least forty trees, only three or 
four feet apart, found in 1838, standing erect upon the wpper surface 
of a seam of coal fifteen inches thick in the railway tunnel at Clay 
Cross, five miles south of Chesterfield; these had no traces of large 
roots, and their exterior consisted of a thin film of coal, furrowed 
and marked like a Sigillaria reniformis ?, the interior being occupied 
by fine-grained sandstone. Mr. Bowman considers the trunks of 
fossil trees in the coal formation, which are thickened at their base, 
and terminate in large expanding forked roots, to have been dicoty- 
ledonous, whilst the monocotyledonous trees maintain throughout a 
nearly uniform thickness, and their roots probably consisted of an 
assemblage of succulent fibres ; and argues, that if beds of coal were, 
like modern peat bogs, the accumulated remains of many genera- 
tions of vegetables that grew upon the spot, they may, during such 
process of gradual accumulation, have afforded a surface adapted 
for the growth of the trees in question. He attributes the fact of 
the roots standing above the upper surface of the coal, as we some- 
times see the roots of fir-trees above the surface of peat, to the 
shrinking of the vegetable matter in which they grew, and considers 
the actual thickness of each bed of solid coal to be about one-third 
that of the vegetable mass from which it has been derived*. 
* JT wish to correct an errorinmy Address of last year (p. 230), where it 
is stated, that the place of the roots of the upright trees discovered in the 
Bolton Railway was immediately wider a thin bed of coal; the fact is, that. 
they were all above this coal: the difference is material, for if the roots be 
all above the coal seam, these trees, like fir-trees in a peat-bog, may have 
grown upon the accumulating bed of vegetable matter which is now con- 
verted to coal. 
The theory that coal, like peat, owes its origin to vegetables that grew on 
