C 385 3 
XV. Observations on the Change of some of the proximate 
Principles of Vegetables into Bitumen ; with analytical Expe- 
riments on a peculiar Substance which is found with the Bovey 
Coal. By Charles Hatchett, Esq. F.R.S . 
Read June 14, 1804. 
§i- 
One of the most instructive and important parts of geology, is 
the study of the spontaneous alterations by which bodies for- 
merly appertaining to the organized kingdoms of nature have, 
after the loss of the vital principle, become gradually converted 
into fossil substances. 
In some cases, this conversion has been so complete, as to 
destroy all traces of previous organic arrangement; but, in 
others, the original texture and form have been more or less 
preserved, although the substances retaining this texture, and 
exhibiting these forms, are often decidedly of a mineral nature. 
Some, however, of these extraneous fossils (as they are called) 
retain part of their original substance or principles, whilst others 
can only be regarded as casts or impressions. 
From the animal kingdom we may select, as examples, the 
fossil ivory, which retains its cartilage;* the bones in the Gib- 
raltar rock, consisting of little more than the earthy part or 
• I have also found the cartilage perfect, in the teeth of the mammoth. 
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