398 Mr. Hatchett’s Observations on the Change 
The Bovev coal is commonly of a chocolate-brown, and some- 
times almost black. The quality and texture of it are various 
in different strata, from some of these, it is obtained in the form 
of straight flat pieces, three or four feet in length, resembling 
boards, and is therefore called Board Coal. Others have an 
oblique, wavy, and undulating texture, and, as Dr. Milles ob- 
serves, have a strong resemblance to the roots of trees, from 
which, most probably, this sort has in a great measure been 
formed. 
Some kinds also appear to be more or less intermixed with 
earth ; but that which produces the most powerful and lasting 
fire, is called stone coal ; it is black, with a glossy fracture ; has 
little or none of the vegetable texture; is more solid and compact 
than the others, being almost as heavy as some of the pit coals, 
the nature of which it seems very nearly to approach. 
For chemical examination, I selected some of the coal which 
had a wavy texture, and rather a glossy fracture ; the quality of 
this sort being apparently intermediate between the others, as 
it retains completely the marks of its vegetable origin, while, 
at the same time, it possesses every perfect character of this 
species of coal. 
i ’ 
solidity of vegetable bodies, produced in the manner imagined by Bergmann, and, 
together with some degree of superincumbent pressure, a real and powerful mechanical 
action has been exerted, by the contraction of the argillaceous strata, in consequence 
of desiccation ; this, I believe, has not hitherto been "much considered, but I am 
inclined, from many circumstances, to attribute to it a very great degree of power. 
