DIMENSIONS OF THE GRAND RAPID. 469 



tage path, I ascertained the fall between the smooth 

 water at the head of the rapid to the general level of the 

 water at the east end of the portage to be 28*58 feet ; 

 and after observing instrumentally the descent in the 

 lower portion of the rapid as far as the nature of the 

 country would allow, I closed my levels on a bench- 

 mark at the surface of a pond of still water, fed by an 

 eddy at the lower end of the portage. The fall in the 

 lower portion of the rapid, acquired by leveling and by 

 careful estimation, is about 15 feet; this would give 43^ 

 feet as the total descent of the rapid. 



3. Its Breadth and Depth. — The width of the river, at 

 the upper end of the portage, is about 20 chains ; at 

 the head of the rapid, about 7 chains further down, 

 where there is an island in the bed of the river, it is 

 about 30 chains ; and at the lower end of the portage, 

 where the rapid emerges from the highest limestone 

 plateau, its width is about 10 chains. From thence it 

 gradually widens towards the foot of the rapid, where it 

 attains a width of 25 chains. I was unable to obtain 

 soundings of the rapid, but, from the depth and volume 

 of water above and below it, where the river is much 

 broader, it is undoubtedly deep. 



The Grand Eapid, throughout almost its entire length, 

 washes the bases of perpendicular escarpments of rock. 

 It passes through two plateaux of brittle buff-coloured 

 limestone, with a horizontal stratification ; the top of the 

 first,- or upper plateau, being nearly on a level with the 

 surface of the water at the head of the rapid, and under- 

 lying a stratum of light-coloured clay, twenty-three feet 

 in thickness, in which are embedded boulders and pebbles 

 of limestone ; the whole overlaid by about eight inches of 

 vegetable mould, and clothed by a forest of balsam- 

 spruce, tamarack, and poplar. The surface of this plateau 



H II 3 



