Mr. McConnell, in his report, enters very thoroughly into this phase of the question. He writes:—“The tar sands evidence an upwelling of petroleum to the surface unequalled elsewhere in the world, but the more volatile and valuable constituents of the oil have long since disappeared, and the rocks from which it issued are probably exhausted as the flow has ceased. In the extension of the tar sands under cover the conditions are different, and it is here that oils of economic value should be sought. In ascending the Athabaska, the tar sands are overlaid at Boiler rapid by a cover of shales sufficient to prevent the oils from rising to the surface, and in ascending the river, this cover gradually thickens. The geological attitudes of the shales is not the most favorable, as the beds dip away from the outcrop at the rate of five to ten feet to the mile, and it is possible that a part, or even the whole of the oil may have flowed northwards and eastwards through the sands, and escaped where these come to the surface. It is unlikely, however, that all the oil has escaped in this manner, as small anticlinals in the covering beds are almost certain to exist, and a differential hardening of the beds themselves may serve to enclose reservoirs or inverted basins of large capacity. It is also possible that the sands at their outcrop may, by the deposition of tarry substances, be plugged tightly enough to prevent further egress. Favourable indications of the presence of oil in the vicinity of the Athabaska are also afforded by the existence of the natural gas springs.”
Mr. McConnell proceeds to show that “Indications of the presence of oil in the district are not confined to the tar sands, as on Peace river and Lesser Slave lake inspissated bitumen was found in a number of places lining cracks in nodules, and at Tar island in Peace river small quantities of tar are brought to the surface by a spring. Tar springs are also reported from several other places, but their existence lacks verification.”
In his Summary Report of the operations of the Geological Survey, for the year 1894, Doctor G. M. Dawson, the director, referring to Mr. McConnell’s explorations and report, wrote:—“The occurrence of great quantities of bitumen or maltha along a portion of Athabaska river has long been known, having been noticed and commented upon by the very earliest travellers in the region. Beds of sand or very soft sandstone of Cretaceous age, varying from one hundred and forty to two hundred and twenty-five feet in thickness, are there found to be more or less completely saturated with bitumen, for a distance of some ninety miles along the river. These beds are known as ‘tar sands.’ More recently a number of smaller occurrences of bitumen in the form of ‘tar springs’ as well as sources of combustible gas, have been found at different places over a very extensive district. All these circumstances point to the probable existence of a great petroleum field, of which possibly some parts have already exhausted themselves in saturating the lowest Cretaceous sands, but of which probably the greater portion is still effectually sealed by the thick covering of overlying rocks. It is believed that the source of the petroleum which has given rise to the deposits of bitumen is in the Devonian strata, which here immediately underlie those of Cretaceous age.”