542 PROCEEDINGS OF NEW y<.|;k MEETING. 



along it- bowlder-filled channel with bewildering impetuosity. At several points 

 small side streams fling themselves over the brow of the unworn cliff's and curve 

 gracefully down into 1 1 1 « - stream beneath. Six miles above it- mouth the gorge is 

 interrupted by a fall 50 feet in height, and a mile further up is closed completely by 

 a fall of 100 feet. A.bove the falls the river has failed to produce more than a feeble 

 impression on the hard limestone beds which floor the Burrounding country, and l< 

 it- valley almost altogether. 



The Bay river falls owe their origin to precisely the same cause as that which pro- 

 due- the famous falls at Niagara, viz., the superposition of hard limeston > soft 



shales, and the consequent undermining and destruction of the formeT effected by the 

 rapid erosion and removal of the supporting beds. It is interesting to And that the 

 rate of retrocession of the two Bills, measured by the length of their gorges, has been 

 almost precisely the same. The quantity of the work done by the two streams can- 

 not, however, be regarded as much more than a coincidence, as the factors in the two 

 as are entirely different. The volume of water which falls over the precipice at 

 N agara is ten-fold greater than that carried by Hay river, while it- erosive power is 

 relatively less on account of its greater purity. Besides Hay river, a number of 

 un- which join the .Mackenzie from the south and Bouthwest in the lir-t 100 miles 

 of it.- course are interrupted by falls and heavy rapid-, all of which probably date 

 from tic- glacial period. 



Proceeding down the Mackenzie from Great Slave lake, alluvial clay- are noticed 

 for some miles, and then a bowlder clay, scarcely distinguishable in character from 

 the same formation as developed in eastern < lanada 3.000 miles distant, makes it- ap- 

 pearance. It occurs here as a light yellowish, compact, arenaceous clay filled with 

 rounded Archean bowlders and. as elsewhere, showing only faint signs of stratifica- 

 tion. It i- traceable in numerous exposures as far as the mouth of the Liard, which 

 joins the Mackenzie l">o miles from it- head. 



The Liard which joins the Mackenzie from the west, affords an excellent cro — eotion 

 of the glacial beds covering the country between the latter river and the mountain-. 

 These do not, however, present much variety. Heavy sections of bowlder clay rest- 

 ing on the Devonian limestones occur along the valley for the first 50 miles, and then 

 sink beneath the Burface; and in the next reach of 60 or 60 miles the river winds 



through oi f th filled up preglacial depressions which are bo frequently met with 



..ii the area ..I' the Great Plains. In this the ordinary lake deposits only are seen. 

 West of this basin the Cretaceous Bhales, which have now replace, 1 the Devonian 

 li m. --lone-, rise to the Burface but arc cap pel with stratified Bhales, sands, and gra\ els 

 only, the bowlder clay having disappeared. Glacial erratics, on the other hand, ex- 

 tend far beyond the limits of the bowlder clay itself, and are found in Bome abundance 

 as far weal as the eastern edge of the plateau country, which in this latitude borders 

 the foothills of the Rocky Mountain-. They were also found on the flanks of a 

 in, .in, tain- ituated opposite Port Liard, in lat. 60° 15' N\, long. 128 \\'.. at a height 



of 1 ,600 feet above the Burfai f the surrounding country, or about 2,800 feet above 



the 



> the Mackenzie and continuing on our way down it. we find bowlder 



claj on the surfa f the rocks and tilline; up irregularities in tl Id preglacial 



-,!,■ ir north as the head of its delta in latitude 67 I / N , and this notwith- 



nding the fact that lesi than 1 < m > miles below the mouth of the Liard the Mackenzie 



enters the fl ol the Rocky Mountains; and for the next 600 or 600 miles 



partially guarded on tl aat by ranges of mountain-, Borne of which ex- 



