NON-METALLIC MINERALS. 
105 
raised only at Bovey Tracey, in Devonshire. The value of 
lignite as a fuel is far inferior to that of ordinary pit-coal and 
the “ Bovey coal ” is practically unused. The plants from the 
Bovey Tracey lignite deposits will be found in the Upper Gallery, 
Case 52. 
Jet appears to be a compact variety of lignite. At Whitby the 
jet occurs in the upper-lias shale. It is found on the shore, 
being frequently thrown up after storms, and is also worked 
inland. Much of the common jet is now imported from Spain. 
Jet is the gagates of Pliny, a name derived from the river Gagas 
in Syria. 
With the coals are introduced a few minerals, or rather rock- 
substances, which, although differing essentially from coal, never- 
theless possess considerable economic value. Of these the most 
interesting is the Torbane Hill mineral or Bog Head cannel from 
the coal measures of Linlithgowshire. From this substance, which 
is well known as having been the cause of considerable litigation, 
were obtained, by distillation at a low temperature, certain hydro- 
carbons highly valued, partly for illuminating purposes and, 
partly as lubricating agents. It is now, however, virtually 
worked out, and recourse is had to other oil-shales in the district. 
The so-called Kimevidge coal is a bituminous shale occurring 
in the Kimeridge clay of Dorsetshire. Small circular discs of 
this shale are frequently found in the Isle of Purbeck, and pass 
under the name of Kimeridge coal money , but it is probable 
that they are simply the refuse pieces from which rings or 
armlets have been turned. 
Hatchettine or mineral tallow is a hydro-carbon occurring in 
the nodules of clay ironstone from the South Wales coal-field 
while Ozokerite or mineral wax is a substance of very similiar 
composition, found in considerable quantity in Moldavia, where 
it has long been used by the peasants and whence it is now' 
largely imported for the production of paraffin and the manu- 
facture of candles. Closely related to thi se are the substances 
grouped together under the general name ot Bitumen or mineral 
pitch. The compact variety called Asphalt is represented by 
specimens from the mountain limestone of this country, and 
from the celebrated Pitch Lake of Trinidad. In this lake, which 
is a mile and a half in circumference, the bitumen is solid and 
cold near the shores, but gradually increases in temperature and 
softness towards the centre, where it is boiling. The ascent to 
the lake from the sea, a distance of three-quarters of a mile, is 
covered with a hardened pitch, on which vegetation flourishes. 
The Elaterite or mineral caoutchouc is a soft elastic variety 
of bitumen having a peculiar odour, and occurring in the 
carboniferous limestone of Derbyshire, where it w T as first observed, 
at the forsaken lead mine of Odin, by Dr. Lister, in 1673. 
Passing over a small group of mineral resins, found chiefly in 
deposits of lignite, the only other min eral which need be noticed 
in this section is the well-known substa nee Amber. The vegetable 
e 87039 , 
F 
