218 
THE GEOLOGIST. 
dred and fifty-five to tkree hundred and fifty-two feet in heiglit above 
the level of the lake. At that part of the island near Manitonwaning 
there is a lake of an hour-glass shape, possessing an area of fifty-five 
square miles (the area of the whole island is sixteen hundi'ed square 
miles), associated with which there is a pecuharity, especially 
described by Mr. Murray. He found that this lake was one hundred 
and fifty-five feet above Lake Huron, and the " question of interest 
connected with this lake, which constitutes its peculiarity, is the 
source whence it derives its supply of water." Mr. MuiTay found 
but one small stream to be its visible supply ; and although thus 
receiving so scanty a tribute from the surrounding country, it fur- 
nished water for three large brooks, which fall from it to the south, 
the west, and the north. These supply several lakes, ponds, and 
streams, among others, Tecumseth Lake, the level of the water in 
which was found in the early part of August to have been much 
higher than it must have been in the spring or some later period. 
This great island consists chiefly of the Niagara limestones ; and as 
this is known frequently to give subterranean passage to streams, 
Mr. Murray thinks it probable that such a communication may exist 
between these lakes, and that there may be others in connection with 
them, and thus the water of Tecumseth Lake may arise from the 
drainage of a considerable part of the island. 
It is possible that further investigation may develope some inter- 
esting facts in relation to these subterranean communications, and 
lead to the discovery of actual caverns. It is earnestly hoped that 
the labour of investigation may be undertaken by persons residing on 
the island. 
29. — Murray's Cavern and Subterranean River, Ottawa, (See 
Map, pi. X. 
This very singular cavern exists at the fourth chute of the Bonne 
Chere river, one of the tributaries of the Ottaway river, recently ex- 
plored by Mr. Murray, of the Canada Geological Survey. At the 
chute a portion of the water turns abruptly off at right angles to the 
general course, running northerly for about ten chains through a 
great cavern formed in the Trenton limestone of the Lower Silurian 
formation. Mr. Mirrray describes the cavern as naturally nearly dry, 
except during freshets. Mr. C. Merrick, an enterprising proprietor 
of the cave and its vicinity, has caused a dam to be thrown across 
the main body of the stream, near the middle of the chute, which 
turns a sufficient quantity of water through to convert the channel 
into a mill-race, and the fall from the lower end is thus advan- 
tageously applied to drive the water-wheel of his mill.* The strata 
of Umestone and shale exposed near Mr. Merrick's mill are in all 
forty-six feet thick, and well charged with fossils, of which Mr. Bd- 
lings gives a list of siKteen Trenton, four Black river, one Birdseye, 
* Geological Survey of Canada, Report for 1853, p. 77. 
