29 
words on the mode of constructing the model. Plans were 
frequently inadequate to convey a correct idea of the state 
of the case, and that was particularly so in the Forest of 
Dean, owing to the steepness of the beds, and the position 
of the coal. The highest veins in geological position could 
not, in some places, be worked without pits, while the lowest 
coal, in other places, could be worked by levels. With a 
view of explaining these phenomena, this model was con- 
structed for the Commissioners of Woods and Forests. It 
might at first appear to be a matter of mechanical difficulty 
to obtain the required shapes without carving. The method 
resorted to was a simple one, and he hoped would be adopted 
in other districts, where gentlemen possessing the necessary 
information might combine, and with little trouble, might pro- 
duce a model like this. First, the information of such gentle- 
men must be collected from a great number of places in the 
district, of which it could with certainty be said, there are 
certain seams of coal at such a depth ; and then, by combining 
such information, relating to different points, and reducing 
it to direct lines, the sections of the principal parts might 
thus be drawn on slabs of wood one-eighth of an inch thick. 
These were " half-lapped" together, to form a sort of net- 
work, or skeleton of the model. What was known having 
been marked on these, the parts must be filled up with judg- 
ment by those acquainted with the district. Having a cer- 
tain number of facts, they must draw their inferences from 
them, so as to shew the bearings in a tangible form, where 
they had not been ascertained by workings. When these 
had been drawn on the blocks by a draftsman, the slabs 
must be taken to pieces, and sawn in portions, having been 
previously numbered, so that they might again be put in 
their proper positions. They might then be put together 
again by a workman, and the interstices filled up with pieces 
of solid wood. When any particular phenomenon occurred, 
