OF CENTRAL CANADA PART V. 309 



deposits and still more recent accumulations. The Cambrian strata 

 comprise representatives of the Potsdam and Calciferous formations ; 

 and the Lower Silurian series or " Cambro-Silurian " of the present 

 Survey is made up of Chazy, Trenton, Utica, and Hudson River 

 beds. These strata, as a rule, are practically horizontal, or dip at an 

 angle only of two or three degrees. 



The Potsdam strata are mostly brown, red, and white sandstones, 

 with some quartzose conglomerates and a few interstratified beds of 

 dolomitic limestone. They form a more or less continuous belt of 

 no great width, curving from the St. Lawrence, below Brockville, 

 north-westerly to the township of Bedford, and from thence in a north- 

 easterly direction to Pakenham on the Ottawa. Instructive exposures 

 may be seen on the river bank between Brockville and Prescott,* 

 at Charleston Lake in the township of Escott; in the vicinity of 

 Perth (where Protichnites and Climactichnites impressions, figures 

 116, 117, occur); at Otty Lake in Drummond ; and at various 

 places in the township of Nepean, where the formation is represented 

 by a white, fine-grained sandstone. Fossils are rare, but at some 

 spots, the small, narrow-beaked brachiopod, lingula acuminata, and 

 the still problematical " scolithus cavities," are present in the sand- 

 stone beds. The Protichnites and Climactichnites impressions occur 

 more especially on ripple-marked sandstones in the immediate neigh- 

 bourhood of Perth. 



The Calciferous strata, which consist chiefly of dolomitic and sandy 

 limestones the " bastard limestones " of the country parlance ex- 

 tend over a considerable area along the inner edge of the Potsdam 

 belt more especially in the Counties of Leeds, Grenville, Lanark, 

 Carleton, and Russell. The principal fossils in these strata, comprise, 

 a small narrow lingula, L Mantelll ; a low-spired gasteropod 

 Euomphalus (or Ophileta) compacta ; some Pleurotomarice, not unlike 

 fig. 219 ; and the orthoceras 0. Lamarki. Exposures occur on the 

 river-bank near Prescott ; at Smith's Falls and elsewhere on the 

 Rideau canal; and at various points in the townships of Oxford, 

 Young, and Edwardsburg; but throughout its extent it is much 

 obscured by overlying Drift deposits. 



* Near Brockville, at several spots, the lower Potsdam conglomerates may be seen to rest 

 unconformably on Laurentian gneiss. A small outlier of these conglomerates was observed 

 by the writer under similar conditions at the western extremity of the gneissoid belt near 

 Gananoque. 



