Great Lake Basins of the St. Lawrence. 268 
waves, as well as by the forces of the atmosphere. These 
reefs also extend a short distance eastward of Owen Sound. 
Two or three miles to the eastward of these cliffs Com- 
mander Bolton has found at least two abrupt elevations quite 
near to the surface and covered with loose rocks. 
Whether, however, there has been any special subsidence 
in the strata on the eastern side of the escarpment or not, 
the escarpment itself has been the subject of elevation, 
greatest at the edge of the cliff and gradually lessening to 
the westward on the Bruce Peninsula, and to the southward 
on the Manitoulin Island, until all of the strata are lost under 
the waters of Lake Huron proper. The soundings along 
the whole eastern coast of the lake from Cape Hurd to 
Goderich, and southward, and off the southern coasts of the 
Manitoulin Islands, show that the strata continue to slope 
gradually towards the central parts of the lake. 
‘ Another somewhat parallel escarpment occurs on the west 
side of Matchedash Bay, and along islands at the extremity 
of the peninsula there. This is, however, in the area of the 
Trenton and Black River limestones, near or at their junc- 
tion with the Laurentian rocks. The strata slope from 
Nottawasaga Bay upward to Matchedash Bay, where they 
present bold cliffs facing to the north-east. The depth of 
water adjacent to the cliffs on these islands is very consider- 
able, reaching a maximum of 267 feet. 
The central and southern deep-water basins of Lake Huron 
are readily distinguished, The former, which is the deeper 
of the two, lies in the Upper Silurian strata, and is separ- 
ated from the latter, which rests on the Devonian rocks, by 
a well defined escarpment evidently of Corniferous limestone. 
This escarpment, starting from the Canadian side south of 
Kincardine, crosses Lake Huron in a north-westerly direc- 
tion in, generally, a line with the Straits of Mackinac until 
near Presqu’isle Point, where it approaches the shallower 
waters of the Michigan coast. If 180 feet in depth of water 
were uniformly removed from Lake Huron, it would com- 
pletely separate these two basins and leave the summit of 
this separating ridge in some cases 120 feet above water. 
