227 
Having hazarded the conjecture that amber has existed, as a bitu- 
men in a fluid state, and that the foreign substances it contains were 
introduced in it whilst it was in that state, it may be expected that 
some instances should be adduced of its having been found in an 
intermediate state between that of fluidity and that in which it is 
supposed constantly to exist. 
But it must be considered that the characteristic physical pro- 
perties of amber, such as yielding a peculiar odour, and becoming 
attractive by friction, depend on its indurated state, and must 
therefore be sought for in vain, in an inferior state of inspissation. 
To ascertain with precision, therefore, from what species of liquid 
bitumen it is derived, may be impossible; since we are reduced, 
whilst seeking for the analogous fluid bitumen, to trace it by the 
aid only of such physical properties as colour, degree of trans- 
parency, &c. which are common to both states. By these marks, 
perhaps, if the substances had been examined with a view to that 
inquiry, some analogy might have been discovered between amber 
and those bituminous masses found by Stelluto, and those said to 
resemble mastich and frankincense, which are described by Dr. 
Woodward and Mons. Fontaine, and which were found even incor- 
porated with fossil wood, with which substance, we have already 
seen, amber is found generally associated. Were such specimens 
again to be foimd, it would be, certainly, highly desirable to ascer- 
tain whether, by continued exposure to a slightly increased degree 
of temperature, or by long keeping, it would acquire the hardness 
and other properties of amber. 
A specimen of elastic bitumen from Castleton, in Derbyshire, 
which I possess through the kindness of Mr. Mawe, shows that 
this variety of bitumen, in a soft state, may possess the colour as 
well as the transparency of amber. It exists in a piece of lime- 
stone, to which it adheres very closely. Its transparency is almost 
that of the clearest amber, and the colour which is most generally 
