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billed action of a portion of caloric ; and, secondly, by conveying to 
every point of the vegetable substance the leaven of the bituminous 
fermentation ; by the active energies of which fermentation the whole 
mass of solid wood is made to undergo an actual conversion, and to 
pass from the state of wood to that of bitumen. 
This particular species of fermentation may be illustrated, by con- 
sidering the phenomena which result from vegetable matter being 
placed in such circumstances, as we have assumed necessary to the 
production of this fermentation, excepting only that of not being in 
a subterranean situation. Should we find that vegetable matter thus 
disposed undergoes a somewhat similar fermentation, producing a 
change approximating to that which takes place in what I have termed 
the bituminous fermentation, we shall have another presumptive evi- 
dence of the propriety of distinguishing the process by which peat is 
formed, as a species of fermentation. 
The situation in which we find vegetable matter thus disposed, and 
in which the effects are immediately under our own examination, is 
that in which the various species of grass, &c. are so closely stowed 
together, and in such quantity, that the weight and thickness of the 
superior layers must totally prevent all access of the external air, 
and any escape of the separated gases. You must have already 
perceived, that I here refer to the process employed in hay-making ; 
and you well know, that when this operation is conducted according 
to the wishes of the farmer, that the saccharine fermentation, or a 
fermentation nearly resembling it, only takes place ; and the grass is 
changed into hay, which possesses a peculiar fragrance and sweetness. 
But should the grass, at the time it is heaped together, unfortunately 
retain too much water, very different effects will follow : heat will be 
rapidly evolved, and a dense vapour will be seen to exhale from the 
mass. If the process be stopped in this stage, the mass of vegetable 
matter will be found to have acquired a very dark brown colour, and 
a glazed surface, and to emit a strong peculiar odour, resembling 
