806 PSOIESSOS TTKDALL ON THE O-EINBD STEUCTrSE OE GLACIEES. 
the toning down of the ridges to rounded undulations which sweep in cur^ns across the 
slacier applies here also. Referring to the section of the glacier of the Rhone m fig. 
ft will be Ln that the word “dirt” is written opposite to each hoRow. In fact t e 
depressions between the protuberances are, to some extent, the coU^ectois of th 
superficial dirt. This is also the case upon the Glacier du Geant ; but here I nonc«l 
that the frmtd slopes of the protuberances were also covered with a fine blown mu . 
tw« down the gfacier the swellings disappear, but the diri retains its position upon 
the ice, and afterwards constitutes the of the Merde Glace. 
A r;markable change in the form of the bands occurs where the g acmr is fo erf 
through the neck of the valley at Trelaporte. They sweep across the Glacier du Gean 
in gentle curves with their convexity downwards; but in passmg Trekporte 
the curves are squeezed more closely together, the vertices are pushed sharply fon ai 
so that on the whole the bands resemble a series of hyperbolas which tend to coincide 
'"LUMiTo™ the Convercle upon the Glacier du Talhfie, a series of swellings 
like those^upon the Glacier du Gdant ai'e observed. Along the mteiienmg ho ow. 
streams run, and sand and dirt are collected, forming the rudiments, so to speak, ot 
series of dirt-bands ; but these latter never attain anything like the precision ot os 
upon the Mer de Glace. I saw no such bands upon the Lechaud, for here 
icifall is absent : if bands at all exist on this glacier, they must, I imagine, be ot a , 
rudimentary and defective character. _ 
I will nol occupy the time of the Society in describing my various expeditions i p 
Glacier du Geant in connexion with these bands ; but one cncuinstance, to which 
"e printing of the bands is mainly due, must be mentioned. The Glacier du Geant 
lies neariy north and south, being only 14 degrees east of the true north, s an 
ing with his back to the Col du Geant, an observer looks northwai-d, and conseqiie . 
the frontal slopes of the protuberances to which I have referred ‘f; 
They therefore retain the snow upon them long after it has been me e lom i ,, 
ral surface of the glacier. The summer of 1867 was unusually warm m the Alps, bit 
its great heat was not sufficient entirely to remove the snow. No doubt, m cok ei sum 
mel, the snow is retained upon the slopes all the year round. Now tins snow become 
the collector of a tine brown mud, which is scattered over the siu-tace ot the glacie • 
catches the substance transported by the little rills and retinns it. le e ge 
snow still remaining, when I was on the glacier, w-ere exceetogly black ; 
in many cases the entire surface of the snow appeared as ri fine peat '“^em 
strewn over it. Lower down the glacier this snow melts, but it leaves its s 
behind it, and to this sediment the distinctness of the dirt-bands ot the Mer e x ace is 
“The regularity of the bands depends on the regularity with which the glacier is broken, 
and the ridges o^r terraces formed as it passes over the brow of the tall. It is the touuig 
down of these ridges which produces the undulations, which are to some extent mo i- 
