280 PEOl'ESSOK TYNDALL ON THE -STSINED STErCirEE OE GLACIEES. 
Grimsel thence to the glacier of the Rhone, thence to the great Aletsch glacier, in 
:: sr 
the Lpedition by a visit to the Mer de Glace and its tributaries, and a second ascent to 
‘^Trint pi^lrahis the evidence derived from the sources thus opened to me ; 
and I shall take these sources in the order in raid c—ve' 
-oted . the select of structme the 
paper contains others on the cause of the/n«»»y of the -''’f “ f “ 
the problem of glacier motion, and on the ongm and cause of the Dut-bands 
Mer de Glace. ^ Qeneral A^ect of the Veined Structure. 
The general appearance of the veined structure is well known. The ice of glaciers^ 
especiaUy midway between their mountain sources and their extremities, is of a wlnt sh 
hue owing to the number of small air-bubbles enclosed in the mass-the lesi , 
doubtless of that ail- which was originally entangled m the snow of which the 
composed Through the general whitish mass, however, at some places, blue i eins ai 
drZ, so n„n.erous indeed in some cases, as to cause the blue ice to Pfedominata o e 
the white A laminated appearance is thus confen-ed upon ‘It® t<=e, the cause of 
Iteness being, that for some reason or other, the bubbles distributed thi-oughoiit the 
general mass do not exist in the veins, or exist there in much smaller numbeis. 
In different glaciers, and in different portions of the same glacier, these vems exirt . i 
different stages of perfection. On the clean walls of some crevasses, and in the Aaim s 
worked in the ice by glacial streams, they present a most beautiful appearance. Tliev are 
not to be regarded as a partial phenomenon, or as affecting the J 
to a small extent only. Vast masses of some glaciers are ; 
greater part of the Mer de Glace, and its tributaries, is composed of this lalinnated ice. 
Ihe lower portion of the glacier of the Rhone, from the base of the ice cascade doun- 
wards is entii-ely composed of it, and numerous similai- cases might be cited. 
' to observe the structure of a glacier it is not even necessary to - the bh™ 
Those who have ascended Snowdon, or wandered among the hills of Cumbe . . 
Tn walked in the environs of Leeds or other towns in Yorkshne and Lancashir^ 
the stratified sandstone of the district is used for ai'chitectm-al purposes ud _ 
observed the exposed edges of the slate rocks, and of the stratified sandstone to 
grooved and fuKowed by the action of the weather. In fact some portions of such loAs 
withstand the action of the atmosphere better than others, and these more resisting 
" stand out in ridges while the softer portions between them -J- ^ 
An effect exactly similar is observed upon the surface of the glaciei. The Ian . 
