716 
ME. HOPKINS ON THE THEOEY OE THE MOTION OF GLACTEES. 
pate in the cases we are considering, will be much less than 45°, the greatest Talue to 
which it can attain when the transverse pressure B predominates over the longitudinal 
pressure A. The lines of marginal structure will be as represented in fig. 7, by the con- 
tinuous portions of the oblique lines. 
Fig. 7. 
43. Formation of the Longitudinal Structure. — If B, the transverse pressure, be very 
great, ^2 sutficient to develope the veined structure in the central as well as the 
marginal parts of the glacier. The curves of structure will then be continued towards 
the axis of the glacier, to which they will constantly converge as an asymptote, as repre- 
sented by the discontinuous lines in fig. 7. If B be very large, the lines of structm-e, 
when examined only in a limited area, will be sensibly parallel to each other and to the 
sides of the glacier. 
44. Formation of the Transverse Structure. — Let us now suppose the longitudinal 
pressure A to be very great, as it must be, for instance, at the bottom of an ice-fall. 
We may also suppose it much greater than B. We shall then have 
tan 2 o5= — A— 
and consequently 2a will either be a small negative angle, or positive and nearly equal to 
180°; and therefore a will either be small and negative, or positive and nearly equal 90°. 
The former must, from the nature of the case, correspond to the direction of maximum 
pressure, and must therefore be and the other aj, as in fig. 8. ag will =0° at 
Fig. 8. 
Q. 
the axis, and will be greatest at Q and K. If A be sufficiently great, the curve of 
structure will be continued across the glacier, constituting the transverse structure. 
45. There are two cases connected with the formation of the transverse structure at 
the bottom of an ice-fall which ought to be noticed. It may happen that the valley 
below the fall shall be an elongated slowly converging valley, or, as occurs perhaps more 
rarely, a rapidly diverging one like that already described at the extremity of the Rhone 
