ME. HOPKINS ON THE THEOET OE THE MOTION OE GLACIEES. 719 
mum pressure between B and D would be very great, and that its direction would be 
nearly perpendicular to that of the motion of the glacier. Consequently the direction 
of the veins, according to the pressure theory, ought to coincide approximately with the 
direction of the motion, as represented by the lines between B and D. The example, 
as I understand it, presents no difficulty in the pressure theory*. 
50. The transverse structure is well developed near the bottoms of the ice-falls of the 
upper part of the Glacier du Geant, and that by which the ice is precipitated from the 
glacier of Talefre to that of Lechaud ; but the most striking exhibition of it is afforded 
by the lower end of the Khone glacier, which has already been mentioned (art. 30) as 
affording an excellent example of longitudinal, or, more properly, radiating crevasses. 
The curves of structure, according to the law above stated (art. 48), are perpendicular 
to the crevasses, and therefore coincident with the surfaces of greatest pressure, as they 
ought to be according to the pressure theory. 
51. The longititdinal structure is perhaps best developed below the junction of the 
Finsteraar and Lauteraar glaciers, where they form the glacier of the Aarf. The mar- 
ginal structure is well exhibited along the flanks of both the tributaries, and is con- 
tinued along those of the combined glacier resulting from their union. It is from the 
point of junction O, flg. 11, and on each side of the axis Ox, that the longitudinal 
structure is so flnely developed. The tributary B A represents the Lauteraar glacier. 
The oblique lines on either flank represent the marginal structure, which is supposed to 
extend only to a certain distance from the sides. The whole width of the glacier of 
the Lower Aar is much less than the sum of the widths of its two principal tributaries, 
so that the transverse pressure (especially near the axis), for some distance below the 
* I may remark that I see nothing distinctive in the observations made by Principal Eoebes on La 
Brenva to determine the relative velocities of points at chiferent distances from the side of the valley. 
Exactly similar results would be obtained on any glacier in which the velocity of the central should be con- 
siderably greater than that of the marginal portions. 
t Ttxdall’s ‘ Glaciers of the Alps,’ p. 387. 
5 F 2 
