24 E. W. ELLS ON THK POTSDAM AND CALCIFBROUS 



about iive and a half miles east of Ottawa city, a prominent escarpment of this rock rises to 

 a height of forty or iifty feet. The strata have a slight dip to the southeast and can be 

 readily recognized from a distance by their white colour. They present, over a large part of 

 the outcrop, a surface of bare rock and pass southward into the overlying members of the 

 Calciferous formation, without any break in the stratigraphy, the beds being perfectly con- 

 formable throughout and the passage from the sandstone upward being quite regular. Owing 

 to the drift of the river valley the next outcrop does not appear till we approach the Rivière 

 du Lièvre. Here on the level at the foot of a sand and clay terrace, lying to the north of 

 the line of the Canadian Pacific railway, the characteristic whitish sandstones are seen and 

 can be traced eastward for nearly half a mile. They are capped by Calciferous beds, the 

 transition upward being gradual, but the contact of the latter with the Laureutian is not 

 observed owing to drift sand. 



On the Lièvre river near Buckingham station, about seventy yards below the bridge, 

 ledges of typical Potsdam sandstone rest upon the gneiss and limestone of the Lau- 

 rentian, and fill up inequalities in the underlying rocks. The basal portion of the 

 Potsdam at this place consists of a conglomerate made up of the pebbles of the Lauren tian 

 in a siliceous paste, the pebbles ranging in size up to several pounds in weight. East of this 

 the typical sandstones are not exposed on the north side of the Ottawa for nearly thirty 

 miles, or to a point about two miles west of the village of Montebello, but Calciferous ledges 

 appear at Thurso, nine miles east of Buckingham, resting directly upon the Laureutian, as 

 also along the road between Thurso and Nation river. At Eockland on the south side of 

 the river, midway between these two places, a regular series of formations from the Lauren- 

 tian to the Trenton can be seen, and the section here is a most interesting one. N'ear the river, 

 at the mills, Potsdam sandstone occurs in low lying horizontal ledges surrounding a boss of 

 Laureutian gneiss and limestone, which dip at a high angle a short distance back from 

 the shore. Near this outcrop of the Laureutian the basal beds of the Potsdam are seen 

 to be made up of the debris of the older rocks. The Potsdam forms a low ridge which 

 23asses upward into the Calciferous, the beds of which are well exposed at a number of points, 

 and in fact underlie the greater part of the village of Rockland. To the south of this the 

 characteristic green shales of the Chazy come in upon the Calciferous, and these are in turn 

 overlaid by the limestones of the Black River and Trenton formations which form a con- 

 spicuous blufl", extending for some miles in an east and west direction at a distance of only a 

 few hundred yards south of the Ottawa. 



The outcrop of Potsdam west of Montebello is also directly and conformably overlaid 

 by the Calciferous beds, and these are again well seen on the south side of the river where 

 they surround a small but interesting outlier of the Laureutian, situated opposite the village 

 of Montebello in the township of Altred. 



Below this place Potsdam sandstones were not recognized till we reach the village of 

 Lachute, though a small outcrop is referred to in the Geology of Canada near Calumet, 

 below the mouth of the Rouge river. At Pointe au Chêne, however, five miles west of 

 Calumet, Calciferous fossiliferous ledges rest directly upon the Laureutian, the I'otsdam being 

 concealed. 



At Lachute, the Potsdam outcrop is in a clift' of fifty to sixty feet in height, a short 

 distance east of the village, with a south dip of four degrees. This is directly and conform- 

 ably overlaid by the calcareous beds ofthe Calciferous, which are seen in another small ridge 



