202 A POPULAR EXPOSITION OF THE 
cially around Ottawa City; but they occupy a still more extensive 
area on the west side of the Laurentian belt, already so frequently 
alluded to as separating the Silurian deposits of the basin between 
the two rivers, from the same deposits of the region west of Kingston. 
In this latter district, they form the north shore of Lake Ontario to 
the neighbourhood of Cobourg, and stretch northwards into the town- 
ships of Loughborough, Portland, Camden, Hungerford, Madoc, Mar- 
mora, and Dummer; and northwestward along the southern outcrop 
of the Laurentian rocks up to near the mouth of the River Severn on 
Georgian Bay,—a line of small lakes occurring for a great part of this 
distance between the highly-tilted gneissoid strata and the nearly 
horizontal Black River and Trenton beds. From a little west of 
Cobourg, the other or more westerly limit of the Trenton outcrop 
runs also to the north-west, and comes out on Georgian Bay a short 
distance west of Collingwood. The whole of Lake Simcoe, with Bal- 
sam, Rice, and other smaller lakes, lies thus within the Trenton area ; 
but the country is much covered by drift deposits, so that exposures 
of rock are not of very frequent occurrence except along the northern 
limit of the formation as given above, and at these points, the Black 
River or lower subdivision is chiefly exposed. The upper or Trenton 
beds, on the other hand, come out chiefly on Lake Ontario. Still 
farther to the west, the formation runs across the northern portions 
of Manitoulin Islands, and is also seen in Lacloche, Mississague, the 
Snake, and other smaller islands, along the north shore of Lake 
Huron. It occurs finally on the north part of St. Joseph Island at 
the entrance of St. Mary’s River. The underlying sandstone of this 
island, as well as the sandstone beds of Sault Ste. Marie, formerly 
referred to the Potsdam series, are now looked upon as representatives, 
in this region, of the Chazy formation. 
In Eastern Canada, exposures of the Trenton Group occur more 
particularly at and around the village of Caughnawaga, on the south 
bank of the St. Lawrence; at Point Claire ; around Montreal; on 
Isle Jésus, Isle Bizard, &c.; at St. Lin, and in the environs of that 
village; at St. Rocque and other places on the Achigan, as well as 
on the rivers Naquarean, Bayonne, and Chaloupe, and here and there 
between these points and the River St. Maurice; at various places in 
the seigniories of Portneuf, Deschambault, and La Chevrotiére; at 
Pointe aux Trembles on the St. Lawrence ; Quebec and its vicinity ; 
around the Montmorenci Falls; on the River Ste. Anne; at Cape 
