180 NEW YORK STATE MUSEUM 



may thus arise a banding of the clay deposits, in which coarser, 

 thick rock-tiour hiyers near the ice margin represent day additions 

 and lliiinuM', liner, more nnctuous chiys represent niglit deposits. 



The control thus exerted will be confused or lost where the 

 waters discharging from different ice fronts reach the area of 

 clay deposition through a common distributer after journeys 

 a half day's stream travel in difference of length. In this case, 

 the day discharge of one stream may deposit at the same time as 

 the night discharge from another stream. A similar disturb- 

 ance or nullification of the differences of day and night discharge 

 must take place in the Rhone valle^^ where tributary glacial 

 streams at varying distances from Lake Geneva have their clay 

 load delivered to the lake several days after the start of the 

 journe}'. Where the clay load of day discharge from one glacier 

 near the head of the Rhone passes a tributary fed by a glacier 

 lower down the valley at night, the day load of one becomes 

 mingled with the night load of the other; and thus the difference 

 between day and night conditions in glaciers which do not dis- 

 charge immediateh' into clay-depositing areas will not" have their 

 diurnal changes recorded in the clay areas to which they con- 

 tribute. As regional glaciers draw their frontal discharge of 

 water from longer distances than valley glaciers such as those 

 in the Alps, it is probable that there will be less difference 

 between day and night discharge at the front in the former than 

 in the latter, for the reason that some of the day water of the 

 inland ice may reach the front only after half a day's journey, 

 thus tending to equalize the outflow. For all these reasons, it 

 is probable that except in the case of the discharge of a single 

 glacial stream into a limited area of clay deposition, diurnal 

 changes of temperature will exert little control over those varia- 

 tions in clay laminae which are characteristic of glacial rock- 

 flours. 



Annual change of temperature and its effect on glacial clays. 

 Summer is the time of glacier melting, winter the time of arrest 

 of melting if not of actual freezing of glacial waters. The sum- 

 mer discharge of glaciers is prevalently pebbly and sandy; the 

 winter discharge is prevalently clayey, for the streams may not 

 then be vigorous enough to carry sand and pebbles out to the 



