OF CENTRAL CANADA PART V. 319 



" grey-band " and beneath the limestone containing shells or casts of 

 the brachiopod Pentamerus oblongus (fig. 193) are given to the Clin- 

 ton Formation. Exposures occur, chiefly, on the Well and Canal and 

 elsewhere in the vicinity of Thorold also, with greatly increased 

 thickness, immediately around Hamilton ; in road-cuttings at Dun- 

 das ; in the gorges of the Noisy and Mad Rivers in Nottawasaga : 

 at spots on Beaver River ; and at Cape Chin, Cape Commodore, 

 and Cabot's Head on Georgian Bay. The celebrated "Thorold 

 cement " is manufactured from a limestone of this Formation. 



Glacial and Post-Glacial Deposits : The greater portion of the 

 Lake Ontario District is overlaid by clays, sands and gravels of the 

 Glacial and Post-Glacial periods. Beneath these deposits, many 

 strata, limestones especially, are seen when first uncovered, to be 

 striated and polished by glacial action. The striae run in some 

 places towards the south-west, and in others towards the south-east ; 

 and the same rock-surface occasionally exhibits both S.W. and S.E. 

 striations. These so called superficial deposits admit in ascending 

 order of the following subdivisions : (i.) Boulder Clay formation ; 

 (ii.) Erie Clay formation ; (iii.) Saugeen Clay and Sand formation ; 

 (iv.) Artemisia Gravel formation; (v.) Algoma Sand formation; and 

 (vi. ) Recent deposits, proper, as shell-marls, bog iron ore, and peat. 



The Boulder Clay or " Till " consists of thick beds of boulder- 

 holding clay, without subordinate stratification. The boulders vary 

 in size from small pebbles to masses of considerable dimensions ; and 

 they consist for the greater part of gneissoid and other crystalline 

 rocks brought down from the Archaean northern region by glaciers 

 or icebergs during the long period of cold which more or less immedi- 

 ately preceded the existing epoch. See ante, page 207. Many of 

 the included boulders, even those of small size, shew marks of polish- 

 ing and striation. In some places, especially on ridges and high 

 lands within the district, the Drift is represented by accumulations 

 of boulders alone, without accompanying clay. Stratified clays, also 

 holding boulders in some localities, overlie the unstratified drift clays 

 very generally, and are known as " Erie clays." They are more or 

 less calcareous, and yield white or light-coloured bricks. Deposits 

 occur at North Toronto, Cobourg, Belleville, Dundas, and numerous 

 other places within the district. The so called Saugeen clays (which 

 yield red bricks) and their accompanying sands succeed the Erie clay 



