160 Mr Bowman on the Fossil Trees found on the tine df 



fore leave no room to doubt that a similar process then took 

 place. It must not, however, be lost sight of, that the fossil 

 trees were standing more or less upright, and immersed in, 

 though not covered by, water. 



After the immersion of the trunk, the boughs and top 

 would remain exposed to the heat and humidity of the at- 

 mosphere, and under these unnatural circumstances the tree 

 would by degrees lose its vital energy and die. Its dead 

 branches would fall off and leave the wood exposed to decay, 

 wiiile the mud from the turbid waters would be forming a 

 compact sediment round the trunk ; incipient fermentation of 

 the bark would soon commence, bitumenization would suc- 

 ceed, and at length it would be converted into coal. The 

 carbonization seems never to have extended to the wood in- 

 wards, nor the decay to the bark outwards ; it being clear, 

 from the regular wavy lines seen on good decorticated speci- 

 mens, that both processes have been arrested precisely at the 

 union of the liber and the alburnum. I think it, therefore, 

 probable that, considering the half-immersed state of these 

 trees, they would struggle for some years between life and 

 death till their tops were quite destroyed, or till they became 

 completely immersed by a second subsidence. The carboni- 

 zation of the bark would probably not take place Where it was 

 not surrounded by sediment ; and this may explain why 

 boughs and branches are not found in upright fossil trees. 

 Every part above the carbonized line would soon perish. 



AVe have, then, in these upright immersed trunks, so many 

 hollow cylinders or moulds, ready to receive the sediment from 

 the turbid waters. The process of filling up would commence 

 as soon as the top of the broken trunk decayed below the sur- 

 face of the water, and the wood was sufficiently removed to 

 admit the deposit. The mud first admitted would be of the 

 same quality as that suspended in the water at the time ; if 

 no change took place before the cylinder was full, the included 

 column would be of one kind ; but if, during the process, the 

 sediment, from being argillaceous became arenaceous, the 

 lower part of the trunk would be shale and the upper sand- 

 stone. As many alternations would appear as in the equiva- 

 lent deposits above, but at a lower level ; and the line of sepa- 



