12 
MUSEUM BULLETIN NO. 23 . 
Rice Lake basin. The present stream in the southern portion 
of this valley is only about 100 feet wide with a maximum depth 
of about 3 feet. The valley in which the stream flows is generally 
nearly a mile wide. It is in places rock-floored and strewn with 
boulders. The sides of the valley are frequently undercut and 
the valley as a whole shows marked evidences of powerful stream 
erosion (Plate II). Where Indian river enters Rice lake a 
large delta, which is only slightly submerged at the present level 
of Rice lake, fills the wide bell-shaped mouth of the river and 
extends for some distance out into the lake. This delta could 
not have been built by the present stream for the stream is 
too small and its valley was so thoroughly scoured by the ancient 
river that little sediment was available for transportation. 
It is, therefore, evident that this delta is to be correlated with 
the ancient Algonquin river. 
Another large delta occurs, as noted by Coleman, along the 
Otonabee river at Peterborough. A lake, which Coleman named 
Lake Peterborough, was formed in the vicinity of Peterborough 
when the drainage was largely diverted from the Indian River 
valley to Otonabee valley by differential uplift. Between Peter- 
borough and Rice lake, drift hills blocked the drainage and for a 
time held the lake up. Laminated clays were first deposited in 
the lake. These were followed by delta sands and gravels which 
are thicker and coarser in character in the northern portion of 
the basin than in the southern portion. The lake was drained 
by the cutting of a relatively narrow and deep valley through the 
range of drift hills and ridges which had blocked the drainage. 
It is probable that the Otonabee River valley carried part of the 
outflow of Lake Algonquin for a short time during the u two- 
outlet” stage of the lake before the discharge was entirely di- 
verted from the Trent outlet by uplift. This seems to be borne 
out by the size of the outlet channel along the Otonabee River 
valley, for it is apparently somewhat larger than could be account- 
ed for by the present drainage. The Indian River valley was, 
however, the main channel of outflow. Lake Peterborough and 
the Otonabee outlet channel are not shown on the accompanying 
map because their correlation with Lakes Algonquin and Iro- 
quois appears doubtful. 
