OF CENTRAL CANADA PART V. 329 



throughout the country between the Grand River and Georgian Bay, 

 and is seen near Brentford and elsewhere to overlie the blue or Erie 

 clay. In many parts, again, of the Erie and Huron district (as in 

 the more western portion of the Lake Ontario region, already described) 

 the brown clays, or in their absence the underlying deposits, are 

 capped by lacustrine sands and gravels, some of which contain shells 

 of fresh-water mollusca species of unio, cyclas, amnicola, valvata, 

 planorbis, physa, limnsea, melania, &c. still inhabiting our lakes 

 and streams ; and similar shells are occasionally found in the clay 

 beds. Terraced deposits containing fresh-water shells of this kind 

 occur especially around Niagara Falls. Other examples have been 

 seen in the vicinities of Paris, Brantford, Walkerton, &c. In addi- 

 tion to these Glacial and Post- Glacial accumulations, various deposits 

 of still more recent origin occur within the district. The principal 

 comprise : the sandy flats of the Grand River and other streams ; the 

 beds of shell- marl which underlie and margin most of the swampy 

 areas ; the ochre deposits of the counties of Middlesex and Norfolk ; 

 and the peat beds of Humberstone and Wainfleet on Lake Erie. 



THE MANITOULIN DISTRICT. 



This district may be regarded as an outlying portion of the Ontario 

 and Erie districts combined, the Silurian strata of these extend- 

 ing into it, and ranging continuously throughout its area. It comprises 

 the Great Manitoulin Island, eighty miles in length, lying along the 

 north shore of Lake Huron, with the La Cloche and other smaller 

 islands between the Manitoulin and the Lake Huron coast, and 

 Cockburn Island, St. Joseph's Island, Canipement d'Ours, &c., farther 

 west. Drummond Island belongs also, geologically, to the district, 

 but lies beyond the Canadian boundary. The more northern portion 

 of the Great Manitoulin contains numerous lakes, and its north shore 

 is indented by comparatively deep bays. These appear to lie in 

 synclinal folds, formed by a series of undulations (with north and 

 south axes) which traverse the Island throughout its length.* The 

 strata of the district succeed each other from north to south, the 



*See "Reports on the Manitoulin Islands," by Dr. Robert Bell, by whom these anticlinals 

 were first pointed out, in Geological Survey Reports for 1866 and 1867. 



