THE SUCCESSION OF DEPOSITS. 45 



other following the general trend of the St. Lawrence 

 valley. The boulder-clay which rests on these striated 

 surfaces is a dark-coloured till, full of Laurentian 

 boulders, and holding Leda glacialis, and also Bryozoa 

 clinging to some of the boulders. In ascending the 

 Murray Bay river, we find these boulder-beds surmounted 

 by very thick stratified clays, with marine shells, which 

 extend upward to an elevation of about 800 feet, when 

 they give place to loose boulders and unstratified drift. 

 About this elevation, the laminated clays meet a ridge of 

 drift like a moraine, crossing the valley, which forms the 

 barrier of a small lake. Petite Lac, and a second similar 

 barrier separates this from Grand Lac. If the valley of 

 Murray Bay river was occupied with a glacier descending 

 from the Laurentian hills inland, which are probably here 

 3,000 to 4,000 feet high, this glacier or large detached 

 masses pushed from its foot, must have at one time 

 extended quite to the border of the St. Lawrence, and at 

 another must have terminated at the borders of the two 

 lakes above mentioned. 



On a still larger scale the N.W. and S.E. striation 

 appears in the valley of the Ottawa, and farther west 

 between the head of lake Ontario and lake Huron, in the 

 valleys descending from the Laurentian plateau. Here it 

 may be ascribed in part to general ice-laden currents 

 from the north-west, and in part to portions of the great 

 Laurentide glacier. 



A most important observation bearing on this subject 

 appears in the Eeport of Mr. R Bell, in the region of 

 lake Nipigon, north of lake Superior. He observed there 

 the prevailing south-west striation, but with a more 

 westerly trend than usual. Crossing this, however, there 

 was a southerly and S.E. set of striae which were observed 



