OF CENTRAL CANADA PART V. 



323 



limestones are overlaid by terraces of fresh-water clay and sand of 

 Post-Glacial age) ; also on the Welland Canal near Thorold ; along 

 the upper part of the escarpment or " mountain " by Grimsby, 

 Hamilton, Dimdas, Ancaster, Rockwood, etc. ; 011 the River Credit 

 in Caleclon, as at Bellefontaine and elsewhere, and on the Nottawa 

 and Beaver Rivers, where it forms high and precipitous cliffs ; at 

 various other points in Mulmur, Nottawasaga, Artemisia, and Eu- 

 phrasia ; about Owen's Sound ; and at Cape Paulet, Cape Chin, and 

 the upper part of Cabot's Head. In the immediate vicinity of Rock- 

 wood, some large caverns occur in a dolomitic limestone (thickly 

 interspersed with, crinoid stems) belonging to this formation ; and 

 deceptive veins and strings of galena have been noticed in the same 

 township (Eramosa), as well as in the Niagara strata of Mulmur 

 and Clinton. 



The Guelph Formation is represented for the greater part by white 

 or light-coloured dolomites of a peculiar semi-crystalline or granular 

 texture, containing, among other fossils, large casts of a lamellibran- 

 chiate mollusk, the Megalomus Canadensis (fig. 210). The coral, Am- 

 plexus laxatus (fig. 143) ; the brachiopod, Trimerella acuminata (fig. 

 1:01) ; several species of Murchisonia, Holopea Guelphensis (fig. 224); 

 and Phragmoceras Hector (fig. 229), are also characteristic. The 

 formation extends over a considerable area, chiefly in the counties of 

 Waterloo, Wellington, and Grey, but it is greatly concealed by over- 

 lying Drift and other superficial deposits. The principal exposures 

 occur on the River Speed in the vicinity of Guelph ; at Elora, near 

 the junction of the Grand and Irvine Rivers, where the strata form 

 high cliffs ; also on other parts of the Grand River, as at Fergus, 

 Preston, and Gait ; near Hespeler, again, on the railway between 

 Guelph and Brantford ; and on the rocky Saugeen River in Bentinck. 

 At most of these localities excellent building-stones are obtained. 



The Onondaga or Gypsiferous Formation consists, in Canada, of 

 thin-bedded dolomites of a yellowish or pale grey colour, associated 

 with greenish calcareo-argillaceous shales and with large masses or 

 irregular beds of gypsum. These deposits appear to have been largely 

 formed from precipitates thrown down in* ancient salt-lakes or bays 

 in which an active evaporation was going on. They contain only a 

 few obscure traces of organic remains ; but hopper-shaped and 

 prismatic casts, derived from crystals of ordinary salt, soluble- sul- 



