68 
Proceedings of the Boyal Society 
The experiments on firwood confirm what we know about the 
difference in conduction along the different axes. 
The experiments on cotton wool by no means refute what Peclet 
has found, viz., that the conduction is the same to whatever degree 
the wool is compressed, thus leading to the most interesting con- 
clusion, that the conductivity of the fibre is the same as that of air, 
and that the conductivity of air is the number given above. The 
very low conductivity of many of these substances are proverbial ; 
more especially flax, which we find at the bottom of the list. Horns 
and hoofs have also a bad name. The makers of boiler cement are 
well aware that they could have worse conductors, but they must 
consider the expense. 
In all these experiments I was much assisted by Mr James 
Gfuthrie, one of my laboratory students. 
3. On the Formation of Coal, and on the Changes produced 
in the Composition of the Strata by the Solvent Action 
of Water slowly percolating through the Earth’s Crust 
during long periods of Geological Time. By R W. 
Thomson, C.E., F.RS.E. 
( Abstract .) 
The author commences by adverting to a very generally recog- 
nised geological difficulty — -viz., that of accounting for the dis- 
appearance of the mineral from the carbonaceous matter in the 
processes which have resulted in the formation of coal-beds as we 
now find them. Coal-beds have undoubtedly their origin from 
decaying vegetable matter; and the deposition is unquestionably 
traceable to at least three different sources — viz., the carrying 
down by rivers of drift wood, and its deposition in deltas and 
estuaries at their mouths; the accumulations of dead forest trees, 
&c., falling for successive generations where they had grown ; and 
the growth of peat. But in all of the three methods it is clear 
that the vegetable matter must have been mixed up to a very 
large extent with earthy matter, which earthy matter has since 
disappeared, so as to leave carbonaceous deposits in a com- 
parative state of purity. The explanation of this disappearance 
has hitherto completely baffled geological ingenuity, and the 
