2 THE MEDALS OF CREATION. "Cap. V. 
situated in depressions or basins, as if they had been pro- 
duced by the submergence of woods and forests, in-a swamp 
or morass ; and in many instances the ligneous structure 
is distinct in one part of the bed, while in another the mass 
is a pure black coal, differing in no respect from true coal, 
except that it is less dense. 
Bovey Coal.—One of the most instructive deposits of brown 
coal in England, is that of Bovey Heathfield, near Chudleigh 
in Devonshire, which is of considerable thickness and extent, 
and presents all the characters of a true coal-field; namely, 
beds of carbonized vegetables, alternating with layers of 
clay and marl. The Bovey coal is in the state of bitumi- 
nized wood, the vascular tissue (which is coniferous in the 
specimens that have come under my notice) being appa- 
rent. It is easily chipped or split, and leaves a considerable 
quantity of white ashes after combustion. The layers of 
coal vary in thickness from one foot to three feet; and 
there are eighteen or twenty in a depth of about 120 feet; 
’ this coal-field extends seven or eight miles. No leaves or 
fruits have been discovered; bitumen occurs both in the. 
coal and in the intermediate clays. Calcareous spar, and 
iron pyrites, prevail in many of the strata. In some places 
this brown coal is covered by a bed of peat, in which trunks 
and cones of firs are imbedded. The whole series appears 
to have been a lacustrine deposit ; probably formed in a 
lake, into whose basin rafts of pine forests were drifted by 
periodical land-floods. (Org. Rem. I. p. 327). 
The brown-coal formations on the banks of the Rhine, 
present the same phenomena on a more extended scale, and 
complicated with changes induced by volcanic action. In 
Iceland, where at the present time forests are unknown, there 
are extensive deposits of lignite of a peculiar kind, termed 
surturbrand. 
BD fe ee nk 
a ee ee ee Oh ae 
Jet.—The beautiful substance called Jet, is a compact 
