R. G. MCCONNElL — THE YUKON AND MACKENZIE BASINS. 543 



ceed 4,000 feet in height. The howlder clay or till of the Mackenzie valley, although 

 mostly of the ordinary type, presents some variations. For many miles above Bear 

 river it is exceedingly dark in color and, with the exception of one layer at its base, 

 is almost destitute of bowlders. It has a thickness here of over 250 feet. In other 

 places it exhibits an imperfect stratification, and it frequently holds irregular shaped 

 inclusions of a lead-gray clay, some of which are distinctly bedded. 



The only evidence of an interglacial period observed was the discovery in one place 

 of an intercalation of stratified sands and gravels dividing the bowlder clay into 

 upper and lower parts. This might, however, be due to a purely local cause. 



The bowlder clay throughout the greater part of the valley is overlain by heavy 

 deposits of stratified sands, clays, and gravels, and is underlain by a gravel formation 

 somewhat similar to that which occurs in the same relative position on the plains of 

 Alberta and Assiniboia, and which I have elsewhere called the Saskatchewan gravels ; 

 from which, however, it differs in containing a larger proportion of Laurentian pebbles. 



The few facts observed in regard to the direction of the ice flow in the Mackenzie 

 valley support the theory of Dr. Dawson as to its northerly movement. In the west- 

 ern part of Great Slave lake the direction of the ice current, as previously stated, was 

 due west. Five degrees further north, well marked glacial striae trending N. 15° W. 

 were found crossing the summit of Roche Carcajou. This rock, which must have 

 been completely submerged, rises to a height of 1,000 feet above the surface of the 

 river. Important evidence on the same point is also afforded by the fact that the 

 till near the lower ramparts of the Mackenzie is in approximately the same latitude 

 as the northern boundary of the Archean area to the east, and the gneissic bowlders 

 which it contains must have travelled either directly west or northwest in order to 

 reach their present situation. 



The facts adduced above allow the inference that the ice from the Archean gathering 

 grounds to the east poured westward through the gaps and passes in the eastern flank- 

 ing ranges of the Rocky Mountains until it reached the barrier formed by the main 

 axial range, when, being unable to pass this, it was deflected to the northwest in a 

 stream from 1,500 to 2,000 feet deep down the valley of the Mackenzie and thence 

 out to sea. 



Leaving the Mackenzie for the Yukon, we climb and cross over a couple of ter- 

 races, the higher of which has an elevation of 500 feet above the river or about 000 

 feet above the sea, and then on this route leave all traces of the glacial age behind, 

 although a few miles further north erratics are found fully 1,000 feet higher. In 

 descending the mountains on the west we follow a branch of Rat river through a 

 wild canon cut out of flat-lying sandstones and quartzites, from the mouth of which 

 a level terrace, with fragments of a higher one resting on it in places, stretches west 

 to Rat river. These terraces are much higher than those on the eastern side, and 

 have an elevation of 1,500 to 1,700 feet above the sea. Proceeding down Rat river 

 to the Porcupine, and down the latter through its ramparts, sands, gravels, and silts 

 are found resting on the country rocks, but no bowlder clay nor glacial erratics were 

 anywhere seen. Some distance below the ramparts the vallej of tin' Porcupine 

 widens, and from that on to its mouth it serpentines through a low alluvial plain ele- 

 vated only a few feet above the surface of the river and evidently representing a 

 iilled-up lake basin or former wide dilatation of the river channel. Turning up the 

 Yukon from the mouth of the Porcupine, this river splits up into innumerable chan- 

 nels and, spreading out in places to a width of eight or ten miles, cuts for 75 miles 

 through the same alluvial formation. Above this the valley becomes more contracted, 



