BRITISH ASSOCIATION MEETING AT CAMBRIDGE. 



417 



racterize the deposit or attract attention, are widely distributed in varioua 

 geological formations, and belong to no special geological period. Crys- 

 talline and metamorpliio rocks contain cliapopote and other forms of bitu- 

 men. Eock oil rises in jets from below Silurian, Devonian, and carboni- 

 ferous rocks in North America. Bituminous limestones and schists occur 

 in Ireland in Silurian rocks, and at Caithness in Devonian rocks, and else- 

 where, not unfrequently in the British Islands, in carboniferous rocks. 

 Bituminous schists are important in the Permian series in Germany, and not 

 absent in the New Kcd 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 unburnt 

 carbon, is a valuable fuel. The best and richest 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 appears 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, chiefl}'' 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 Fontenay-le-Comte, situated in the 

 Bourbon Vendee, between Nantes and Ilochelle, 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 paralhne 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. 



Tiie 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 freely, with much smoke and a long llame, 



VOL. V. 3 11 



