500 Mr. J. Ball on the Structure of Glaciers. 
horizontal lines of gravel were seen at intervals, and, as far 
as I was able to get access to them, I was led to the belief that 
these corresponded to the outcrop of surfaces extending into 
the interior of the glacier, and strictly conformable to the direc- 
tion of cleavage. I was not able to cut far into the ice, but it 
appeared to me that the lines of gravel were merely superficial, 
and caused by the slight projection of the edges of surfaces of 
somewhat harder ice retaining minute fragments in their descent 
over the face of the glacier. Subsequent observations made 
higher up led me to doubt the complete accuracy of this conclu- 
sion. The direction of the strike of the cleavage planes, marked 
as it was to the eye by the lines of gravel, and by the occasional 
blue veins, varied a good deal, partly from lateral contortion, 
owing, as it appeared, to inequalities in the rocky bed of the 
glacier, and partly to a variation in the dip, which was nearly 
horizontal, but sometimes inclining outwards at a small angle, 
just as we find it in ordinary glaciers. 
On ascending the glacier, the lower part of the surface was 
found to consist of the same white ice that has been already de- 
scribed, without any trace of veined structure, but having, at 
intervals of from 10 to 15 feet, transverse dirt-lines, evidently 
marking the same structure as the gravel-lines on the terminal 
slopes. Crevasses were pretty numerous, disposed in lines 
radiating from the apex of the cone, and often 6 or 8 feet in 
width. On the walls of these crevasses the dirt-lines were well 
marked, and had all the appearance of being produced by thin 
layers of dust penetrating the ice, but instead of being hori- 
zontal or dipping outwards they invariably dipped inwards, to- 
wards the centre of the glacier, at an angle which increased 
from below until about the middle of the glacier, where it varied 
from 30° to 40°. In no instance was IJ able to detect traces of 
veined structure in the walls of the crevasses. 
Above its middle region the glacier was covered with the 
remains of éboulements, which had taken place during the past 
winter and spring. The surface was irregular, but not so much 
so as I have seen it in places where frequent falls of the con- 
solidated névé take place. Very few fragments of ice were seen, 
and it seemed to me that the greater part of the mass must have 
fallen from the upper region in the state of snow very loosely 
agglomerated. The very fact that this glacier can be traversed 
in summer without danger, is a proof that it is not chiefly formed 
of fragments of ice falling from a higher glacier, as has been in- 
cautiously asserted by Agassiz*, on the authority of M. Desor ; 
for in glaciers of the latter class the surface is covered with large 
* Nouvelles Etudes, p. 242. 
