MINERALS AND GEOLOGY OF CANADA. 449 
in the eruption of Vesuvius in 1861.* The great petroleum springs 
of Central Asia, which have been flowing for ages also, with those of 
Zante (mentioned by Herodotus) and others of different localities, lie 
essentially in areas of volcanic action; and the so-called mud-vol- 
canoes often pour out large quantities of bituminous matter, mixed 
with other products. It might be argued that in these cases the 
petroleum is derived from deeply-seated coal beds, but of this we 
have no proof. And when we consider the fact that small quantities 
of bitumen and petroleum occur in rocks geologically far older than 
those of the coal series, we have an equal right to assume that these 
matters may be generated, without the aid of organic bodies, by un- 
known chemical action within the crust of the earth, and may be 
poured out through fissures from time to time, both amongst deposits 
under process of accumulation, and amongst others already ‘consoli- 
dated.+ [n this manner, I imagine, our petroleum springs of Western 
Canada have originated. And I would go beyond this, and refer to 
the same action a leading part in the formation of all bituminous 
shales, and of coal seams generally. In the latter case, the liquid 
bitumen or petroleum may ke conceived to have flowed into broad 
marshes, or over low-lying districts, in which an abundant vegetation 
was under growth. The vegetable matters thus saturated and mixed 
up with the thickening petroleum, would add their substance to the 
formation of the coal, and would be chiefly instrumental perhaps in 
imparting to this its peculiar character. On this view, the formation 
of bituminous shales by the saturation of the finer kinds of sedimen- 
tary matter by petroleum overflows, becomes readily explained; and 
also. the close agreement in character which exists between the shales 
of the coal measures and those of many Silurian strata. The old view 
does not explain these points in a satisfactory manner. The petroleum 
theory likewise obviates the necessity of assuming the growth of an 
enormous and unparalleled vegetation during tie Carboniferous period; 
and it explains why the vegetation of after periods so rarely yielded 
coal—the outflows of petroleum having chiefly taken place during 
the Carboniferous epoch, and only locally at other times. 
The Portage and Chemung Group.—The rocks of this group, so 
largely developed in the peninsula of Michigan and other districts of 
% Sea Canadian Journal, vol. vii , p. 126. 
+ If the term “ unkuown chemical action ” be here objected to, we may refer, aniongss 
other cases, to that of the diamond: a substance certainly formed by chemical action, but 
ef a kind altogether unknown to us. 
