Mr. J. Ball on the Structure of Glaciers. 501 
iceblocks, which are frequently descending from above, and few 
explorers like to remain longer than they can avoid within their 
reach. A genuine example of this kind is seen on a terrace of 
the Wetterhorn, further removed from the Scheideck than that 
which I visited, and much higher above the valley leading to 
Rosenlani. Circumstances did not allow me to attempt to ex- 
amine it. The ascent would be rather difficult, and the passage 
of the glacier, if at all practicable, would involve some risk, un- 
less made in the early morning, before the ice commonly begins 
to descend from the upper plateaux. 
The upper part of the Schwarzwald glacier has but few cre- 
vasses, and it is therefore difficult to trace the dirt-lines which 
are there covered with the fresh snow fallen from above. I 
was, however, able to convince myself that the inward dip attains 
its maximum about the middle of the glacier, and gradually 
diminishes in the upper part, not exceeding 10° at the highest 
point where I was able to measure it. 
_ I should add, that I had direct proof of the motion of the ice 
in this glacier, though this is probably slight. At the bottom, 
opposite to the centre of the terminal face, a miniature moraine, 
about 30 feet long and 3 high, had been quite freshly thrown 
up by the advance of the ice during the early part of the sum- 
mer, but owing to its rapid waste during a warm season the ice 
had again receded 3 or 4 feet. 
I leave it to more competent authorities to decide on the sig- 
nificance of the facts above stated. To myself, it appears that 
they are not completely reconcileable with any of the hypotheses 
that have been framed to explain glacier structure. If the whole 
phznomenon were one of cleavage in planes dipping inwards at 
the middle of the glacier, and horizontally or outwards at the 
bottom, it might with much plausibility be ascribed to pressure. 
Butif the clear blue veins occasionally present are to be re- 
ferred to the same cause, how is it that the air-bubbles in the 
white ice show no trace of its action? But still more difficult it 
is to understand how any amount of pressure could cause the 
production at regular intervals of those surfaces whose presence 
is revealed by the dirt-lines, whether these are due to the pre- 
sence of dirt * in the mass of the ice or not. 
The advocates of the stratification theory may maintain that 
* The determination of this point would require a sharp cutting instru- 
ment, which I had not with me, and careful examination of the ice with a 
powerful lens. It must be recollected that an exceedingly thin film of dust, 
dispersed over a surface enclosed in a mass of ice, might be scarcely per- 
ceptible, but that the melting of a thickness of several feet of the same ice, 
leaving much of the enclosed dust upon the face of the glacier, would render 
its presence plainly visible to the eye. 
