Notices of Jfenioirs — Vegetation of the Coal Period. 31 



-with seams of coal. Vast areas of coal have been worked witliout 

 any such trunks having been encountered. The majority of the 

 trunks, moreover, are destitute of spreading roots, and are believed 

 to have been floated to their present positions. The land-shells, 

 insect and reptilian remains, are of extremely rare occurrence. 



The underclays do not resemble soils, inasmuch as they are 

 perfectly homogeneous, and lie with absolute parallelism to the other 

 members of a stratified series. They are not always present beneath 

 coal-seams, but, on the other hand, often occur in them or above 

 them. Frequently they have no coal associated with them. The 

 rootlets in them have no connection with the coal, which is a well- 

 stratified deposit with a sharply defined base. 



The persistence of the partings and characters of the coal over 

 ^vide areas is in favour of their being subaqueous deposits, for on so 

 large an expanse of land there must have been river-systems and 

 variations in the vegetation. The stream-beds, known to miners as 

 • wash-outs,' are not proportioned in size to the supposed land- 

 surfaces. 



Subaerial decomposition of part of a mass of vegetable matter 

 would take place whether it were floating or resting on dry land. 

 tSpores, which enter largely into the composition of many coals, 

 would travel long distances either by wind or water. 



Some coal-seams show clear proof of a drifted origin, as, for 

 example, those which are made up of a mass of small water- worn 

 chips of wood or bark. Other seams pass horizontally into bands 

 of ironstone, and one case has been observed of a coal changing 

 gradually into a dolomitic tufa, doubtless formed in a stagnant 

 lagoon. Putting aside exceptional cases, the sequence of events 

 which preceded the deposition of a normal coal-seam seems to have 

 been — firstly, the outspreading of sand or gravel with drifted plant- 

 remains, followed by shale as the currents lost velocity. The water 

 was extremely shallow, and even retreated at times, so as to leave 

 the surface open to the air. The last sediments were extremely 

 fine, homogeneous, and almost wholly siliceous, and in them a mass 

 of presumably aquatic vegetation rooted itself. This further im- 

 pediment to movement in the water cut off all sediment, and the 

 material brought into the area then consisted only of wind-borne 

 vegetable dust or floating vegetable matter carrying an occasional 

 boulder. Lastly, the formation of the coal-seam was brought to 

 a close by a sudden invasion of the ai'ea by moving water. The 

 mass of vegetable matter, often after suffering some little erosion, 

 was buried by sandstone or shale rich in large drifted remains of 

 plants or trees, and the whole process was recommenced. 



Z. Botanical Evidence bearing on the Climatic and other 



Physical Conditions under which Coal avas forsied. By 



A. C. Seward, F.R.S. 



Botanical investigations into the nature and composition of the 



vegetation which has left abundant traces in the sediments of the 



Coal-measures may be expected to throw some light on the natural 



