122 ROYAL SOCIETY OF CANADA 
to seven feet or at the rate of six inches per year. During this time 
the amount of asphalt removed has been not far from 1,500,000 tons. 
In composition the material contains approximately about thirty per- 
cent of water and the same amount of impurity which consists of organic 
matter and sand or earth deposits the remaining forty per cent being 
bitumen, 
Along the shores to the west an interesting illustration of the 
amount of this overflow from the vast body of asphalt of the lake can be 
seen. The lake is situated at an elevation of not far from 138 feet 
above sea-level and at a distance of three-fourths of a mile inland. 
Throughout this distance deposits of the asphalt are seen, sometimes at 
the surface as overflows and sometimes beneath the covering of sand, 
while on the shore itself for a distance of more than a mile along the 
beach large overflows of the asphalt are everywhere visible, outcropping 
from beneath the sand, and these have evidently been derived from the 
main body inland. Good illustrations of flow structure are seen in these 
shore deposits, the asphalt of which is also mined and shipped 
extensively. 
The surface of the lake is hard and can be travelled in all directions 
with carts and horses. In no place is it very soft, but occasionally near 
the centre it is sufficiently plastic to allow the impression of the foot when 
walked over. Along most of the fissures on the surface the peculiar flow 
structure of the mass can be readily seen, the material being drawn out 
in curving lines in a downward sloping direction around the lips of the 
fissures. The slow movement thus indicated in a densely viscid sub- 
stance would apparently imply that the whole or greater part of the 
asphalt was influenced by convection currents and was in a constant state 
of slow motion. The same peculiarity of tension is seen also on 
freshly mined blocks of the mineral, in the presence throughout the mass 
of cavities of various sizes large and small, or what appear to be air or 
gas bubbles. These are elongated or drawn out along the lines of move- 
ment in the slowly moving mass. 
The apparent cause of this slow movement in such a thickly viscid 
deposit, which is practically a solid as regards mining, may be due either 
to displacement of the material through the removal of large portions 
at various points over the surface, or to a possible inflow of thick petro- 
leum from the bottom or from points along the sides of the deposit at 
low levels, from the gradual thickening of which this enormous mass of 
asphalt has been derived. The thickness of the deposit has been tested 
at several points by boring and near the centre at a depth of some 135 
feet the bottom was not found. Nearer the shores, however, the depths 
varied greatly and bottom was reached in several places showing the basin 
