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vegetables necessary to form thick seams of coal could have been 
derived, if drifted ; and how they could have been sunk to the bot- 
tom, without being intermixed with the earthy sediment which was 
slowly deposited upon them. He is of opinion also, that without a 
superincumbent layer of mud or sand, to retain the hydrogen during 
the process of bituminization, ordinary caking coal could not have 
been formed. Another difficulty, connected with the drift theory, 
Mr. Bowman says, is the uniformity of the distribution of the vege- 
table matter, throughout such great areas as those occupied by the 
seams of coal, extending in the instance of the lower main seam of 
the great northern coal field, over at least 200 square miles; and in 
that of a thin seam below the gannister, or rabbit coal, in a linear 
direction of thirty-five miles from Whaley Bridge to Blackburn. 
On the contrary, he believes, that it is much more rational to sup- 
pose, that the coal has been formed from plants, which grew on the 
areas now occupied by the seams,—that each successive race of 
vegetation was gradually submerged beneath the level of the water, 
and covered up by sediment, which accumulated till it formed an- 
other drysurface for the growth of another series of trees and plants,— 
and that these submergences and accumulations took place as many 
times as there are seams of coal. He also explains the thinning 
out of the seams and other strata of the coal measures, by irregu- 
larities in the mode or extent of the depressions. 
Mr. Bowman then proceeds to the examination of the phenomena 
presented by the fossil trees discovered on the line of the Manchester 
and Bolton railway, and described by Mr. Hawkshaw in his paper 
read on the 5th of June 1839, (see p. 139.) and in the preceding 
communication (see p. 269.) : it will be necessary tv notice there- 
fore only those points which did not claim that gentleman’s more 
particular attention. Mr, Hawkshaw describes generally the mark- 
ings on the internal casts of the trees; but as it is difficult to convey 
a correct notion of their waved and anastomosing characters either 
verbally or by reduced drawings, Mr. Bowman applied paper to the 
surface of the stems and carefully traced the grooves or furrows by 
following them exactly with an instrument. The only indications 
of scars, which he could find after a long and close search, were at 
one point near the base of the largest tree, and though indistinct, his 
practised eye recognised them to be those of a Sigillaria. He de- 
tected also in some parts, on the ribs of the same tree, the fine wavy 
lines so often visible on decorticated specimens of that family. In 
describing the second tree, he alludes to a deep wedge-shaped rift 
on the south-east side, which had been coated with coal, and is 
strongly marked with wavy lines, like those on the surface of thé al- 
burnum of a gnarled oak. On the fifth tree, he discovered a longi- 
tudinal concavity on the north side, and he states that it resembles 
the impression which would be left in a dicotyledonous tree, by the 
pressure of a parasitic plant. The characters of the roots are also 
detailed at considerable length, paricularly their mode of bifurcation, 
and position with respect to the horizon. 
From a careful consideration of the phenomena pr esented by the 
¥2 
