254 
INTERNAL STRUCTURE AND 
of course subjected to the same action, and are 
contorted, bent, and folded by the same lateral 
pressure. 
Dr. Tyndall has advanced the view that the 
lines of apparent stratification, and especially the 
dirt-bands across the surface of the glacier, are 
due to ice-cascades : that is, the glacier, passing 
over a sharp angle, is cracked across transversely 
in consequence of the tension, and these rents, 
where the back of the glacier has been succes- 
sively broken, when recompacted, cause the trans- 
verse lines, the dirt being collected in the furrow 
formed between the successive ridges. Unfor- 
tunately for his theory, the lines of stratification 
constantly occur in glaciers where no such ice- 
falls are found. His principal observations upon 
this subject were made on the Glacier du G4ant, 
where the ice-cascade is very remarkable. The 
lines may perhaps be rendered more distinct on 
the Glacier du Geant by the cascade, and neces- 
sarily must be so, if the rents coincide with the 
limit at which the annual snow-line is nearly 
straight across the glacier. In the region of the 
Aar glacier, however, where my own investiga- 
tions were made, all the tributaries entering into 
the larger glaciers are ribbed across in this way, 
and most of them join the main trunk over uni- 
form slopes, without the slightest cascade. 
It must be remembered that these surface-plie- 
