16 
MUSEUM BULLETIN NO, 23. 
species. They were determined by E. M. Kindle, of the Geolog- 
ical Survey, to be Lymnia palustrius Muller, Lymnia decollate 
Mighels? Valvate tricarinate Say, Valvata sincera Say, and 
Sphaerium rhomboideum Say. Mollusca of all these species 
have been found to be living in Georgian bay. 1 No fossil shells 
were found in the sands of the lower portion of the section. The 
shell-bearing sands occur at this locality at altitudes of 730 to 
735 feet above sea-level. Fossil shells of similar species were also 
found in the deposits of the highest shore-line of Lake Algonquin 
near Roches Point and at Wilfrid at altitudes of 775 and 800 
feet respectively. The distinct break in the lacustrine sediments 
shows that the water must have risen. The occurrence in the 
deposits of the highest shore-line of Lake Algonquin of fossil 
shells of mollusca similar to those living in Georgian bay, and the 
fact that the fossil shells are only slightly reduced in size show 
that temperature conditions of the water could not have been 
much more severe than at present. This is also borne out by 
the general absence of ice “ramparts” on the abandoned shores 
of Lake Algonquin and the rare occurrence of boulders in the 
lacustrine deposits of the lake. No fossil shells are known to 
occur in the older deposits of the early stage Lake Algonquin 
before it reached its maximum extent and ice-rafted boulders 
more commonly occur in these deposits, apparently showing a 
more frigid temperature of the water. The magnitude of the 
vertical interval through which the waters rose before reaching 
their maximum extent, as shown by the highest shore-line of 
Lake Algonquin, is not definitely known. In the southern portion 
of Lake Simcoe district it was apparently at least 50 feet, for the 
vertical interval between the base of the fossiliferous sands, which 
show an unconformable relation to the underlying deposits, and 
the crest of the highest Algonquin beach at the nearest locality 
which is on the same isobase is about 65 feet. The magnitude 
of this vertical interval in the southern portion of Lake Simcoe 
district suggests that the rise of the waters was not entirely due 
to uplift of the northern portion of the Algonquin basin and 
consequent drowning of the southern shores of the lake, but 
that a general rise of the lake level took place, due possibly to a 
1 Robertson, A. D., “The Mollusca of Georgian bay,” Sessional Paper No. 39b, 1915. 
