Manchester Fossil Trees, ayid on the Formation of Coal. 213 



former receives much support from the phaenomena presented by 

 the fossil trees found near Manchester, and that it affords in return 

 great assistance in explaining the peculiarities of their position. 

 Mr. Bowman does not deny tliat plants may have been carried into 

 the water from neighbouring lands, as in the instances of fern-fronds 

 and other remains scattered through the sandstones and shales ; but 

 he conceives it is difficult to understand whence the vast masses of 

 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 whicli 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 dry surface 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 phsenomena 

 presented by the fossil trees discovered on the line of the Manchester 

 and Bolton railway, and described by Mr. Hawkshaw in his paper 

 readon theothof June, 1839, (see L. &E. Phil. Mag. vol. xv. p. 539.) 

 and in the preceding communication (see vol. xvii. ji. 541.) : it will 

 be necessary to notice therefore only those points which did not 

 claim that gentleman's more particular attention. Mr. Hawkshaw 

 describes generally the markings 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 in- 

 strument. 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 recognized them to be 

 those of a Sigillaria. He detected 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 



