20 
The American Geologist. 
January, 1896 
per, we cannot effect it without tearing the paper by rents parallel to its 
length, or the direction of movement. Now, such must be the case 
with a mass of ice which does hot move with a uniform velocity in its 
transverse section, but where every line of particles has the velocity 
proper to its position in the ice-stream. The ice will, therefore, be rent 
by innumerable fissures whose general direction will be parallel to its 
motion, and these fissures, becoming filled with water and ultimately 
frozen, will produce the appearance of bands traversing the general 
mass of the ice having a different texture. 
In his later writings Forbes renounced the idea of the infil¬ 
tration and freezing of water along the planes of shearing, 
which produces, indeed, only such exceedingly narrow and 
discontinuous fissures that the whole mass is quite as imper¬ 
vious as portions of the glacier lacking this structure. Nor is 
the delicately veined ice readily cleavable, until in its melting 
the white lamime, which contain plentiful minute air bubbles, 
yield more quickly and are affected to a greater depth than 
the compact blue ice. 
Tyndall especially attributed the veined structure to pres¬ 
sure and insisted on its close analogy with the slaty cleavage 
of rocks. Moving laterally and spreading out at right angles 
from the direction of greatest pressure, the particles compos¬ 
ing the white ice laminae receive nearly all the air which be¬ 
fore was uniformly distributed through all the mass, while the 
blue laminae endure the compression with little differential or 
shearing movement. The origin of the veining in a crevassed 
and recemented ice cascade or fall of a branch of the lower 
glacier of the Grindelwald is described by Tyndall, from his 
observations in 1858, as follows:* 
On the middle of the fall itself no trace of the structure was manifest; 
but where the glacier changed its inclination at the bottom, being bent 
upwards so as to throw its surface into a state of intense longitudinal 
compression, the blue veins first made their appearance. The base of 
the fall was a true structure mill , where the transverse veins were man¬ 
ufactured, being afterwards sent forward, giving a character to portions 
of the glacier which had no share in their formation.What has 
been stated regarding the Grindelwald ice-fall is true of that of the 
Rhone; the base of the cascade is the manufactory of the structure ; 
and, as all the ice has to pass through this mill, the entire mass of the 
glacier from the base of the fall downwards is beautifully laminated. 
According to the place and manner of origin of the blue and 
white lamination, Tyndall noted three distinctions : first, mar- 
* Hours of Exercise in the Alps, 1871, pp. 369-371. 
