PROGRESSION OF GLACIERS. 
263 
horizontal, the few blue hands observed are per- 
pendicular to the strata of snow, and therefore 
also perpendicular to the blue seams of ice and 
the sheets of dust alternating with them. Upon 
the sides of the glacier they are more or less par- 
allel to the slopes of the valley ; along the line 
of junction of two glaciers they follow the verti- 
cal trend of the axis of the mass ; while at inter- 
mediate positions they are more or less oblique. 
Along the outcropping edges of the strata, on the 
surface of the glacier, they follow more or less 
the dip of the strata themselves ; that is to say, 
they are more or less parallel with the dirt-bands. 
In conclusion, I would recommend future inves- 
tigators to examine the glaciers, with reference 
to the distribution of the blue bands, after heavy 
rains and during foggy days, when the surface is 
freed from the loose materials and decomposed 
fragments of ice resulting from the prolonged ac- 
tion of the sun. 
The most important facts, then, to be consid- 
ered with reference to the motion of the glacier 
are as follows. First, that the rate of advance 
between the axis and the margins of a glacier 
differs in the ratio of about ten to one and even 
less ; that is to say, when the centre is advancing 
at a rate of two hundred and fifty feet a year, the 
motion toward the sides may be gradually dimin- 
