blup: bands. 209 



other and stretching part way across the space emhraced in the loop. 

 Here it would seem that the blue bands are produced by the exceptional 

 pressure of the ice in moving over rugosities on the brow of the emboss- 

 ment, and that their position in the ice is parallel to the ice-movement, 

 while at the same time blue bands may also be developed nearly at right 

 angles, after the analogy of slaty cleavage. 



It has already been remarked that the most solid ice was usually 

 observed in immediate association with the lamina? of earthy matter. 

 The inference is, therefore, that the agencies which introduced the earthy 

 material by the same act developed solid ice. Independently of either 

 of these forms, it appeared to be beyond serious question that solidified 

 layers of ice were developed out of the crusts of the original snow, and 

 hence that a variety of the bands is a direct derivative of the original 

 stratification. In so far as the general shearing of the strata upon each 

 other takes i^lace indei)endently of the special process by which earth was 

 introduced, to that extent, I judge, the faces which moved over each other 

 developed greater solidity than the adjacent parts and approached the 

 more perfect ice of the blue bands. I am not sure that these observa- 

 tions traverse in an}' serious way the current doctrine, which we owe to 

 Tyndall, that the blue bands are chiefly the product of i)ressure in con- 

 stricted ]>ortions of the glaciers or in the descent of cataracts, but they do 

 suggest tliat this doctrine needs limitation and qualification. 



Summary. — In a word of summary, therefore, it would ap2)ear that 

 stratification originated in the inequalities of deposition, emphasized by 

 intercurrent winds, rains and surface meltings; that the incipient strati- 

 fication may have been intensified by the ordinary processes of consolida- 

 tion ; that shearing of the strata upon each other still further emphasized 

 the stratification and develo])ed new horizons under favorable conditions ; 

 that basal inequalities introduced new planes of stratification, accom- 

 panied by earthy debris, and that this process extended itself so far as 

 even to form very minute laminie. 



Discussion of Causes of Movements of Glaciers. 



Infliridnality of Ice-lay rrs. — There is involved in the foregoing concep- 

 tions the idea of an ice-layer acting as a unit of movement, or at least 

 individuality of movement in the layer is recognized, an idea that, if cor- 

 rectly entertained, is one of some im])ortance, I think, in the jdiysics of 

 glaciers. This view involves the idea of rigidity rather than viscosity. 

 It will not have escaped attention that the explanation heretofore given 

 of the introduction of earthy material into the ice-la\'('rs involves the 

 idea of thrust rather than i)ull. The picture is not tliat of graviUition 



