MINERALS AND GEOLOGY OF CANADA, 447 
diately above the rock ; whilst the latter are continued into the rock 
itself, to an average depth of from 50 to 150 feet. The discharge 
from the wells is accompanied, in many cases, by salt water, and by 
emissions of inflammable gas. In some of the wells which have 
ceased to yield petroleum, salt water has taken the place of the rock 
oil. 
The fissures or reservoirs in which the petroleum occurs, are appa- 
‘rently of restricted size, and very irregular in their course. Whilst 
in some instances, neighbouring wells affect each other, and thus evi- 
dently draw their supply from the same immediate source, in other 
instances, borings put’ down close to wells in active operation, and 
carried even to a greater depth, have failed to strike the oil fissure. 
The origin of the petroleum is involved in great obscurity. ‘Two 
views have been suggested in explanation of its occurrence. One of 
these connects the presence of the rock oil with the great coal deposits 
of Michigan, or those of Ohio and Pennsylvania. The coal-bearing 
strata of these districts occupy a much higher geological position 
than the petroleum-containing beds of Western Canada. The Penn- 
sylvania coal strata are geologically over 10,000 feet above these 
latter ; and a thickness of 860 feet intervenes between the top of the 
Hamilton formation and the coal deposits of Michigan. A long 
interval of time must therefore have elapsed between the deposition 
of the two series of strata. But the petroleum may have been gene- 
rated in the Michigan beds at some subsequent epoch, and have been 
carried along a system of fissures into our Devonian rocks: the two 
formations, owing to the dip of the strata, occupying very nearly the 
same topographical elevations. Several facts are opposed, however, 
to this view. In the first place, no evidence of the occurrence ’of 
liquid petroleum amongst the Michigan coal seams has hitherto been 
obtained, neither are any reservoirs of petroleum known in coal rocks 
of other localities; secondly, small quantities of petroleum and of 
solid bitumen, (a closely allied substance) occur in various strata far 
below, and topographically far removed from ccal deposits; and 
thirdly, the direct distance between the rim of the Michigan coal 
field and the oil district of Enniskillen is at least 80 miles, so that 
‘the existence of continnous fissures of communication between the 
two is not very probable. 
The second view regards the rock oil as originating within the 
strata in which it occurs, by some peculiar decomposition of fucoids 
