Mr. J. Ball on the Structure of Glaotere. 498 
the effects of pressure arising from the form of the solid chaniels 
through which they move, assumes a degree of elasticity in the 
substance of the ice, which, until it is proved to exist, can 
scarcely be taken for granted. Seeing the extent to which a 
large portion of the mass is penetrated by air-bubbles, omitting 
all consideration of the fissures and crevasses which extend through 
most portions of it, it might be expected that before an intense 
force acting from without could be transmitted so as to modify 
the structure half a mile away from the point at which it is 
applied, it would first exercise such a crushing force upon the 
part of the glacier near at hand as would greatly modify its 
actual structure. If experiment should show that a measurable 
amount of pressure applied to a block of glacier ice does actually 
cause a flattening of the air-bubbles at right angles to the direc- 
tion of pressure, we must conclude that no pressure of equal 
amount has previously been transmitted through that block, and 
we shall be better able to estimate the pressure, from sources 
external to the glacier itself, that can have acted on the interior 
of the mass. My own impression is, that the cleavage which 
is sometimes, but not invariably, developed in the veined struc- 
ture, is produced by pressure acting on ice in which that strue- 
ture already existed, and that it is accompanied by a partial 
flattening of the air-bubbles adjoining the surfaces of the blue 
veins, and in the planes in which cleavage takes place. I do not 
pretend, however, to advance such a conclusion with confidence 
on the strength of such few and imperfect observations as I have 
been able to make. 
One more remark I venture to offer upon a question of fact, 
rather than of theory, though it has an important bearing upon 
the whole question under discussion. 
The accomplished authors of the paper read before the Royal 
Society, starting for the first time to visit the glaciers of the 
Alps, with a surmise that the phenomena of veined structure 
might be accounted for as particular cases of slaty cleavage pro- 
duced by pressure under new conditions, were naturally struck 
by every fact that appeared to confirm that conclusion. They 
noticed instances in which the veined structure, instead of ex- 
hibiting the blue veins in continuous surfaces, showed merely 
flattened cakes of blue ice imbedded in a matrix of white vesicular 
ice. More frequently they found that the blue veims, while 
seldom more than an inch or two in thickness, thin out and dis- 
appear after being traceable for a distance of some feet. Hence 
they have been led to apply the term “/enticular structure” as de- 
scriptive of that which previous observers had called the veined, 
or laminar structure of the ice. So long as the new expression 
was confined to the particular and unusual condition of the ice 
