Mesozoic and Cccnozoic Geology and Falceontology. 317 



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 b}' 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 complanatus, Cyclas dubia, C. similis, 

 Amnicola porata, Valvata tricar inata^ V. piscinalis^ Planorhis trivol- 

 vis, P. campanulatus, P. bicarinatus, Limncea 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. Planorhis 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, woin 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 



