GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



51 



of the ice. Finally the bands mingled with the superficial rock covering of the 

 glacier and were lost. Standing upon an individual band the dark color seems 

 to be imparted by the fine dust and sand and not by the coarser debris. In 

 September, 1905, owing to the excessive melting of the summer, the bands stood 

 out with unusual clearness, so that they w^ere photographed from the side of the 

 Lefroy Glacier, as shown in plate xvi, figure 2. By signaling to an assistant, 

 the well defined up-stream margins of 19 of the bands were located by erecting 

 small cairns of rock, and their distances apart, in the line of their apices, were 

 later measured (see map, plate iii). The results were as follows, beginning near 

 the foot of the ice slope. The average interval between the bands is 97 feet. 



For reasons to be given later the writer believes that the intervals between 

 these bands mark the annual progress of the ice down the slope, as conjectured 

 by Tyndall, and offers the following explanation of the phenomenon. As the ice 

 of the glacier is pushed over the crest of the ridge in its bed, which is responsible 

 for its change in surface slope, there is formed successively a series of transverse 

 crevasses, as explained upon page 36 of this report. The distance between 

 these crevasses will be determined mainly by the thickness of the ice and the 

 change in its angle of slope. Since the glacier is moving foi^ward in winter as 

 well as summer, although at a less rate, these crevasses must originate at all 

 seasons of the ^-ear. Those which have been formed in the late fall, or winter, 

 upon passing down the slope will be perfectly healed, since their lips have ex- 

 perienced practically no melting from the sun's action. The opposite crevasse 

 walls come slowly together, refreeze, and leave no visible scar in the ice. Those 

 crevasses, however, which have formed in the late spring and summer have their 

 lips much rounded by the sun's rays. If the glacier is moving northward as in 

 the case of the Victoria and Lefroy, the northern, or down-stream lip of the 

 crevasse will receive the maximum eftect, the southern comparatively little. 

 Should the glacier be moving southward, the northern lip of the crevasse would 

 still be the one most strongly acted upon by the sun, but in this case it would be 

 the up-stream side. Glaciers flowing east or \\-est, and having their transverse 

 crevasses in an approximately north-south position, would have their crevasse 



