THE PETROLEUM SPRINGS OF WESTERN CANADA. 319 
‘explain the geological structure of the region where the oil springs are 
found, regarding which no uncertainty exists, and which, apart from 
the subject of the oils, is peculiarly interesting. 
Sir William Logan has pointed out that, if we conceive a line passing 
from the head of Burlington Bay through London, Zone, Chatham 
and Amherstburgh—being in fact the centre line or back-bone of the 
Western Peninsula—such line would form what is called, in geological 
parlance, the summit of a flat anticlinal arch; that is, the strata bend 
or dip slightly in an opposite direction on either side of it. In the pre- 
‘sent case the dip is so small as to be almost inappreciable by instru- 
ments ; but it is nevertheless certain that the strata which occupy that 
part of our peninsula now under review pass under the coal measures 
of Pennsylvania on the one hand, and of Michigan on the other, at a 
depth varying from 1000 to 2000 feet ; which thickness of course repre- 
sents, or is the measure of the time, geologically speaking, which 
elapsed between the deposition of the newest of our rocks and the 
carboniferous era. Consequently it is quite evident that we must not 
seek for the origin of the petroleum deposits in the coal formation, 
properly so called. 
The outcrops of the various members of the series of rocks imme- 
diately overlying the Appalachian and Michigan coal-fields form strips 
or belts which are rudely concentric with the coal basins themselves. 
The region now under notice is precisely the tangent point (as it were) 
where the corresponding strata under each coal-field meet and blend 
together, giving to the region occupied by the strata in question a form 
approaching that of the letter X. These rocks are called the Hamil- 
ton Shales, and constitute the lowest member of the Devonian or Old 
Red Sandstone system. Although in this locality of no great thick- 
ness—probably not exceeding 60 or 70 feet—the formation is most 
interesting in a geological point of view, as containing a well-marked 
nd highly characteristic group of fossils, including the earliest known 
traces of terrestrial vegetation and of fishes. The formation consists 
of calcareous shales, with thin bands of denser limestone, and oc- 
casionally beds of sandy limestone, which are valuable for building 
purposes. The shaley portions crumble rapidly on exposure, and form 
a gray or ash-coloured clay; the fossil contents however remaining 
entire. 
At Kettle Point, on Lake Huron, a locality comprised within the 
geographical boundaries of the Hamilton Group, there is exposed an 
