Spencer.] dio [March 18, 



ous limestone looking to the northward, until it was finally undermined, 

 and worn back to its present position, submerged beneath the shallower 

 waters of the southern portion of the lake, or buried in drift deposits. 



On the northern side, the lake has not made so much encroachment, as 

 it is bounded by the hard Niagara limestones of the Manitoulin islands, 

 and the Indian peninsula of Canada, the strata dipping down beneath the 

 lake. Yet it must be noticed that these rocky shores are indented by nu- 

 merous deep bays transverse to their directions. 



The North Channel. This is generall}' a shallow water, the greatest 

 depth being only 204 feet. To the northward, we have the Huronian rocks 

 forming tlie boundary. The islands, especially towards the ^eastward, and 

 near the whole north shore, are generally composed of Trenton limestone. 



Tlie southern margin of the channel, bounded by Manitoulin and the 

 other islands, is often composed of Hudson river, more or less, shaly rocks, 

 overlaid by the Niagara limestones (where not removed by denudation), 

 constituting an escarpment facing the northward. In fact, the whole of the 

 north channel is principally scooped out of the Hudson River Formation, 

 which attains a considerable thickness in this region. 



Dr. Robert Bell states that he has observed fifteen anticlinal folds trav- 

 ersing the group of the Manitoulin islands ; and it is in these that we find 

 the great indentations, and lakes in the islands, as well as the straits which 

 separate them. Doubtless many of the southern ends of the Manitoulin 

 lakes and channels are filled with drift. For example, the mouth of South 

 bay is only 33 feet deep, whilst the upper portion is generally deep, one 

 place giving a sounding of 156 feet. 



In fact, the north channel may be considered as a broad continuation of 

 the Spanish river westward. The Mississagua river points directly to 

 Mississagua straits, which are 204 feet deep, as deep as any part of the 

 channel itself. Thessalon river has a direction towards False Bay De Tour, 

 which is 186 feet deep. Vermilion river flows amongst the islands west 

 of Cloche mountains and probably had a connection to Lake Huron through 

 some of the buried channels across Manitoulin islands, as between Manitou- 

 aning and South bays. 



The narrow channel between the peninsula of Cloche mountains and 

 Manitoulin island is less than 60 feet deep and appears to be a modern con- 

 nection with Georgian bay. 



Georgian Bay. The eastern and northern margins of this bay are com- 

 posed of crystalline rocks ; the south-eastern, of Trenton limestone ; 

 whilst the western is made up of the Hudson River shales capped with the 

 Niagara limestone, on the Indian peninsula and Manitoulin island. This 

 basin is principally excavated out of the Utica shale, and the somewhat 

 harder rocks of the Hudson River Formation. It lies along the junction of 

 the various formations, and thus on the removal of the lower soft layers of 

 rock, an escarpment was produced which has subsequently and slowly 

 continued to be undermined. 



In the channels connecting this bay with Lake Huron, there are many 



