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Mesozoic and Cenozoic Geology and Paleontology. 213 
the edge of the river, and recedes in sweeping curves in both direc- 
tions from each of these points. A bay, two miles and a half in 
depth, is thus left between them, and is occupied by a barren plain of 
no great elevation above the river, partly covered with coarse brown 
| sand, and partly strewn with bowlders of northern metamorphic rocks 
: and angular fragments of Silurian sandstone, which are sometimes 
| arranged in small bare ridges parallel to the present direction of the 
. river. The surface has thus the appearance of having formerly been 
covered with swiftly flowing water. 
To the north of Lake Huron, and between the Georgian bay and the 
Ottawa river, part of the surface of the country consists of bare rock, 
but where any superficial covering exists, it is almost invariably a 
yellow sand. A belt of loose gravel, remarkable for its great extent, 
stretches in a southward direction across the peninsula of western 
| Canada, from near Owen sound to Brantford, a distance of 100 miles, 
. Its average breadth is nearly 23 miles, and its total area more than 
| 2,000 square miles. This great belt of gravel has a general parallelism 
| with the Niagara escarpment, and consists in large part of the ruins 
of the underlying Guelph and Niagara Groups, though pebbles of the 
Huronian and Laurentian rocks are everywhere mixed with the others, 
and fragments of the Hudson River Group occasionally occur. 
| Beside these clays and sands there are several local accumulations 
| in western Canada, often marked by fresh-water shells. These, to- 
gether with various ridges and terraces, which are conspicuous features 
in the surface geology of this region, appear for the most part to have 
been formed by the waters of the great lakes, when their extent was 
much greater than at present. The most considerable deposit of this 
kind is the sandy tract in the county of Simcoe, which extends south- 
eastward from the head of Nottawasaga bay, and has an area of more 
; than 300 square miles. Unio camplanatus, Cyclas dubia, C. similis, 
* Amnicola porata, Valvata tricarinata, V. piscinalis, Planorbis trivol- 
' vis, P. campanulatus, P. bicarinatus, Limnea palustris, and Physa 
ancillaria, occur at from 30 to 40 feet above the level of Lake Huron, 
and twenty miles distant near the Nottawasaga river. Planorbis tri- 
volvis, and three species of Helix, were found in sand and gravel in a 
road cutting through a little ridge between 75 and 78 feet above Lake 
Huron, about a mile south of Collingwood harbor. ‘Two miles west of 
Cape Rich, worn fragments of bark and wood were met with in digging 
a cellar on a terrace 155 feet above the lake. There are several terraces 
of sand and gravel which correspond to ancient water margins on the 
