BRITISH ASSOCIATION MEETING AT CAMBETDGE. 417 
racterize the deposit or attract attention, are widely distributed in various 
geological formations, and belong to no special geological period. Crys- 
talline and metamorpliic rocks contain chapopote and other forms of bitu- 
men. Eock oil rises in jets from below Silurian, Devonian, and carboni- 
ferous rocks in I^orth America. Bituminous limestones and schists occur 
in Ireland in Silurian rocks, and at Caithness in Devonian rocks, and else- 
wliere, not unfrequently in the British Islands, in carboniferous rocks. 
Bituminous schists are important in the Permian series in G-ermany, and not 
absent in the New lied Sandstone. The Posidonia schists of the Lias and 
other beds are highly bituminous, and in the Oolites, the cretaceous rocks, 
and even in the Tertiaries, especially in Germany, the same bituminous 
character often prevails. Asphalte is common in some Tertiaries ; oil rises 
from the nummulitic rocks in the East, and in the West Indies we have 
the Pitch-lake of Trinidad. 
In almost all these cases there is a marked distinction between coal, 
properly so called, and rocks containing the hydrocarbons. Coal is mineral 
fuel, from which gas can be obtained by destructive, and occasionally cer- 
tain oils by slow, distillation. The various bituminous rocks or bitumens 
contained in rocks are not good fuel, but yield largely certain valuable 
products by slow distillation. Coal can be coked, and the coke, or uuburut 
carbon, is a valuable fuel. The best and ricliest of the bituminous schists 
will not coke, and the result of an attempt to make it is to produce an ash 
that will not burn. 
Notwithstanding this general distinction, coal passes insensibly into 
cannel coal, or parrot, and this again nppears to pass into those peculiar 
shales rich in bitumen, known in Scotland as Boghead coal or Torbane Hill 
mineral. These remain debatable ground. Specimens of them, carelessly 
collected, have been used as fuel ; but parts of the same sample are often 
coal, while the rest is shale, and thus much confusion has arisen as to the 
fuel question. They are unusually rich in valuable oils, and form a curious 
passage between two minerals — coal and shale, or schist — that do not ge- 
nerally bear any resemblance. 
The distinction between coal and shale is practically very important, and 
deserves careful consideration. I wish to direct the attention of the Sec- 
tion to some instances that may help to throw light upon the question. 
Two localities in France visited by me in the year 1861 are particularly 
interesting in this respect, and deserve to be better known by English geo- 
logists than they seem to be. The rocks in both are of the carboniferous 
period. The various places where the Lias schists are now worked for dis- 
tillation, chiefly in Germany, are also worthy of special reference, and the 
Tertiary bituminous shales of the Ehine are not less important. 
At Feymoreau, a short distance from Fonteuay-lc-Comte, situated in the 
Bourbon Vendee, between Nantes and Eochelle, there is a small coal- 
field, almost classical in respect to the important distillation of light oils 
by slow distillation of rocks containing hydrocarbons. It was at this spot, 
then far less accessible than it now is, that M. Selligue, so long ago as in 
1830, obtained light paraffine oil, heavier illuminating oil, lubricating oil, 
and paraffine, by a method identical with that patented by Mr. Young in 
England in 1851. The works were abandoned owing to the want of com- 
munication with a market, and M. Selligue afterwards established works, 
still carried on successfully, at Autun. 
The Feymoreau schists underlie coal of a poor quality, and thus replace 
underclay, but they contain no vegetable impressions or markings. They 
are of deep black colour, hard and tough when first exposed, but fall to 
pieces after a time. They burn freol}'-, with much smoke and a long flame, 
VOL. V. 3 H 
