Il8 GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



If the seismic theory furnishes the true explanation of these double massive 

 moraines, then we have a means of correlating the positions of the extremities 

 of all the glaciers showing them at these two stages in their history, also data 

 for determining their actual retreat since and their relative rates. Glaciers, that 

 were not tributary to others at the time, confined between steep cliffs, having 

 a northwest to southeast trend, may be expected to show such moraines. There 

 is the possibility that any particular glacier may have advanced since and have 

 overridden one, or both, as the Victoria and Wenkchemna have partially done 

 with the inner of their series. Numerous earthquakes must have occurred 

 during the long Pleistocene period, but the cliffs were so completely blanketed 

 in snow that we find no such records left in the trunk valleys. Similar moraines 

 should be found in other sections of the world, but they might originate from 

 the removal of the finer materials by running water, as well as by earthquakes 

 and simultaneous rock slides. As to the actual age of these moraines we may 

 only loosely speculate. The blocks look old and the schists and sandstones have 

 disintegrated more or less, in situ, but undoubtedly they were badly weathered 

 before the glaciers got possession of them. The age of the moraines is to be 

 expressed in centuries rather than thousands of years. Based upon our vegeta- 

 tion data we may conclude that the inner of the two moraines was completed 

 about five or six centuries ago and that the earthquake disturbance respon- 

 sible for it may have occurred two centuries earlier. The outer of the two 

 moraines seems to be about two centuries older. 



6. SURFACE FEATURES. 



a. Dirt bands, zones, and stripes. In Chapter III of this report the writer 

 has described and figured these three glacial features and has suggested that 

 certain terms, used rather indiscriminately for any one, be restricted to a single 

 feature. The first two are very often confused, one with the other, but are so 

 essentially different in their real nature, if not always in their appearance, that 

 they should be sharply separated and differently named. The dirt zones, or 

 simply the zones, when the foreign matter is not present to discolor them, are 

 the outcropping edges of the strata of which the glacier is composed. They show 

 to best advantage about the nose and lower margins of the glacier that is suffi- 

 ciently free from debris, as broad, parallel zones encircling the lower extremity 

 and passing around to the sides where they disappear. They are usually convex 

 down-stream, but the form they assume is determined by the configuration of the' 

 glacier's extremity. In case the stratification in the glacier is absent for any 

 cause, there can be no zones seen. 



The dirt bands are entirely superficial and result from the collection of fine 

 debris in long hollows or troughs that first extend transversely across the glacier, 

 but which become convex down-stream from the more rapid central motion of the 

 ice. They occur in series, roughly parallel and regularly spaced, and assume 

 finally a pointed, or hyperbolic form, which probably suggested to Schlagintweit 

 the term "ogiven." The name "dirt band," however, was originally assigned 



