282 PEOFESSOE TYNDALL ON THE TEINED STEHCTHEE OE GLACIEES. 
to the lenticular structure described by Mr. Huxley and myseH, j 
lose themselves as pale washy streaks in the general mass o£ the white ^ . 
have endeavoured to give an idea o£ a very common 
aspect of the veined structure. Such a structure is 
not that which we should expect from bedding. 
Again, taking the Glacier du Geant as a represent- 
ative case, we have first of all the slopes of the Col du 
Geant, the collectors of the snow by which the glacier 
is formed. The fissures on these slopes exhibit beauti- 
fully, to a certain depth, the horizontal stratification. 
The lines of bedding may be seen as far down as the 
summit of the great ice-fall between the Eognon and 
the Aiguille Noire ; and on the castellated masses at the 
summit of this fall, to which the name series has been 
applied, the lines of stratification may be distinctly 
seen. Escaped from the confusion of the fall, the 
glacier flows gently through a long valley towards its 
1 unction with the Lechaud and Talefre at the Tacul. 
I Woughout the entire length of this glacier the planes of the stmetnre are rer >ca^ 
I nearly so ; sometimes they dip a little foiwd, but at other places they p an q 
nnantitv backward Now let the mind figure, if it can, an agency which, as the mass 
rr/s the fau, shai turn up the '>°ri.ontal strata of the Col du Geant ^ 
vertical, without a single break, throughout the entire le^U f 
and I imagine the effort to conceive ot such an agency will be followed by the con 
Hint tbo chanse indicated is inconceivable. 1 1 
Further we often find, in the central portions of a glacier, the structime fee e, o 
aca^cC-lopeHt all, while at the sides it is well developed. Tins is often the case 
where the glaler moves through a valley of tolerably uniform inclination, and whe 
no mell Lraines occui- to complicate the phenomenon. But if the veins nimk the 
! bedding, there seems to be no reason why we should not find them as c eai ) 
I the centre as at the sides ; the fact, however, certainly is that w-e do not 
I Let me here show the true significance of this fact. If a plastic su s an , 
l^ud fl”wLn a sloping canal, the central portions will flow more J 
lateral ones which are held back by friction. Now the flow may be so regulated th • 
cMe stlped upon the central portion of such a inlid-stream shall move donmward 
withemt sensible distortion, thus proving that the central mud is neitiei . 
stretched longitudinally; for if the former the circle would be 
with its major axis transverse to the axis of the stieam, an , „ ’ . .iinilar 
v7 ntif tn an ellipse with its major axis parallel to the hue of flou. 
aWce of longitudinal compression exists in many glaciers, and in such ice-streams t lere 
is no transverse central structure developed. 
