Dr MacCulloch on Peat 
215 
having once been liquid, its charcoal has originally been in a 
state of cliemical combination with the hydrogen. 
Between the chemical composition of coal and lignite, suppos- 
ing the latter perfectly bituminized, there appears no difference ; 
the only sensible one being that arising from the remains of or- 
ganization visible in the latter. By a process of fusion, jet can 
in fact be converted into coal ; or, at least, the slight difference 
which may remain, is that only which arises, from the imperfect 
bituminization of the jet ; a circumstance which does not affect 
this inquiry. 
It remains, therefore, only to discover by what process beds 
of bituminized peat or lignite may have been so condensed as to 
acquire the peculiar compactness and mineral structure display- 
ed by coal ; as the chemical resemblance has been established, 
and as it has been shewn that the former are produced by the 
action of water on vegetable matter. Those who have consider- 
ed the process of bituminization to have resulted from the action 
of fire, have also viewed the peculiar structure of coal as tlie 
consequence of fusion under pressure. The fallacy of the ex- 
periments by which the former circumstance was supposed to be 
establislied, has already been shewn. To determine the pro- 
bability of the latter supposition by a more correct mode of ex- 
perimenting, portions of jet were submitted to the action of fire, 
under pressure so regulated as to admit the escape of such vo- 
latile matter as might endanger the apparatus. Thus the orga- 
nized structure of the jet was destroyed, and the mass was 
brought into fusion. On being cooled, it broke easily into ir- 
regular fragments, not unlike some varieties of coal. In all 
other respects, as might be expected, it bore an exact resem- 
blance to that substance ; and it is also worthy of remark, that 
in proportion to the greater or less facility with which the vola- 
tile matter escaped, the results bore an analogy, sometimes to 
dry, and at others to bituminous coal. 
It does not, however, follow from these experiments, that the 
theory which they seem to support is the true one. There is, 
in the first place, a deficiency of evidence to prove, that the 
secondary strata in which coal is found have been exposed to 
the action of fire. In the next place, although the superincum- 
bent weight of materials would undoubtedly give the degree of 
pressure required by this hypothesis, that pressure is not in it- 
