320 MINERALS AND GEOLOGY 



deposit, and occur more or less all over the Province. Beds of coarse 

 gravel mixed with boulders, known as the Artemisia Gravel forma- 

 tion, occupying a somewhat higher horizon than that of the stratified 

 Saugeen clays and sands, occur especially (as regards this district) 

 along the base of the Niagara escarpment in the townships of Arte- 

 mesia, Osprey, Mulmur, Mono, and Albion, where they form the 

 chief mass of the " Oak Ridges." These latter extend from the es- 

 carpment eastwards, and rise in the township of King and adjacent 

 townships to elevations of from 700 to 760 feet above Lake Ontario. 

 In many places the gravels are seen to be distinctly stratified, and 

 here and there they hold gneissoid and other boulders of large size. 

 The Algoma sands consist of still higher accumulations of white or 

 light-coloured lacustrine sands, practically free from stones or boulders, 

 and often shewing signs of oblique stratification. These lacustrine 

 sands occur extensively throughout the district, as seen along the 

 line of the Canadian Pacific Railway between Toronto and Peter- 

 borough, in cuttings on the Grand Trunk between Scarborough and 

 Hamilton, around Barrie on Lake Simcoe, and elsewhere. Many 

 fresh-water shells (Unio complanotns, Cyclas similis, Planorbis 

 trivolvis, Limncea palustris, etc..) identical with those now living in 

 our lakes and streams, occur at various levels in these and other re- 

 lated beds their presence in these deposits apparently indicating the 

 former union of our lake-waters into one vast fresh-water sea. In 

 this case, the water must have been held up in the east by a greater 

 elevation of the gneissoid belt of rock which crosses the St. Lawrence 

 between Brockville and Kingston, and expands into the wild district 

 of the Adirondack Mountains in the State of New York ; or perhaps 

 by an enormous glacier, descending from the latter region and ex- 

 tending northwards into Canada. The shells of recent species of 

 mollusca found in the Post-Glacial deposits east of this gneissoid 

 belt, belong to marine or brackish- water species : whilst those within 

 the Lake Ontario District, and country to the west, are all fresh- 

 water types. The most abundant of the recent deposits, proper, of 

 this region, are the beds of shell marl which occur at numerous local- 

 ities, forming the floor and margin of small lakes and swamps. 

 This substance is a white or light -coloured calcareous deposit, con- 

 taining minute shells of species of cyclas, planorbis, and other fresh- 

 water mollusca. 



