~ 
WEALDEN COAL. 165) 
probably resulted from an accumulation of plants of less 
firm texture, and more perishable, than those of which the 
former is composed.* 
Many interesting facts relating to the carbonization of 
vegetables, came under my observation during my researches 
in the Wealden strata; and it is a subject of regret to me, 
that circumstances prevented my following up the investi- 
gation of those still imperfectly explored deposits. Small 
nodular portions of coal, in which no structure is appa- 
rent, often occur in the calciferous grit of Tilgate Forest ; 
and sometimes large masses of lignite, fissured in every 
direction, and having the interstices filled with white cal- 
careous spar.t Some of the sandstones are discoloured 
by the abundance’ of minute particles of lignite, produced 
by the disintegration of ferns peculiar to the country of the 
Iguanodon. 
The original structure and composition of a plant doubt- 
less affected its carbonization ; for in the same layer of stone, 
the stems of Hndogenites, hereafter described, invariably 
possess a thick, outer crust, of coal; while those of Clathra- 
rue, plants allied to the Cycads, have not a particle of car- 
bonaceous matter, but are surrounded by a reddish brown 
earthy substance. The nature of the stratum in which 
the plants were imbedded, must also have influenced the 
process of bituminization. Masses of vegetables buried 
_ beneath beds of tenacious clay, by which the escape of the 
gaseous elements set free by decomposition was prevented, 
must have been placed under the most favourable conditions 
for their conversion into lignite and coal. 
That the production of lignite is still going on there can 
be no doubt; and the following instance of a bed of recent 
origin, affords an instructive illustration of the subject. 
* See Dr. Dunker’s Mon. Norddeutch. Weald. 
+ A fine specimen of this kind is in the British Museum. 
