126 THE ICE AGE IN CANADA. 



That strong currents of water have traversed this 

 upper plain, is shown not only by the occasional ridges of 

 gravel, but by the depressions known as " slues," which 

 must have been excavated subaqueous currents. 



Near Medicine Hat a terrace of boulders was seen at 

 an elevation of about 200 feet above the river ; and in 

 sections of the drift observed in coulees, the boulders were 

 seen to be arranged in layers ; but whether these appear- 

 ances had relation to fluviatile action, before the excavation 

 of the deep valley of the Saskatchewan, or belonged to 

 the orignal distribution of the drift, was not apparent. 



Lauren tian boulders were seen all the way to Calgary, 

 but with an increasing proportion of quartzite boulders 

 from the Rocky mountains ; and on the banks of the Bow 

 river were large beds of rounded pebbles which must 

 have been swept by water out of the valleys of the 

 mountains, and are quite similar to those now observed in 

 the bed of the Bow itself. 



Beyond this, Dr. G. M. Dawson has recorded Lauren- 

 tian boulders and fragments of limestone from the eastern 

 Palaeozoic beds, at elevations of from 4,200 to above 5,000 

 feet,* at the foot of the Rocky mountains, evidencing a 

 driftage of at least 800 miles, and an elevation consider- 

 ably above that of the sources from which they came. 

 He well observes that anything which would explain the 



* " Many of these (Laurentian erratics along or near the base of the 

 mountains between the 49th and 50th parallels) lie at heights exceeding 

 4,000 feet, while the highest observed instances of their occurrence are 

 at an elevation of 5,289 feet above the present sea-level, the erratics 

 being here stranded upon moraine ridges due to local glaciers which 

 have flowed out from the valleys of the Rocky mountains, probably 

 during the first maximum of glaciation. These erratics are known to 

 have come a distance of at least 500 miles from the eastward." G. M. 

 Dawson. 



