and Motion of Glaciers. 



387 



and the corner of Trelaporte." Here we are not only informed 

 of the existence of a cascade, but are left to infer that the dirt- 

 bands begin to form at its base, as in the Glacier du Geant, and 

 in those which have come under our own observation. The 

 clean Glacier des Bossons, also, which was referred to by Prof. 

 Forbes, in one of his earliest letters, as affording no lodgement 

 to the dirt, possesses its cascade (page 181) ; and here also we find 

 (page 182) " that the peculiar phfenomena of ' dirt-hands ' on a 

 great scale are not wanting, although from the dazzing white- 

 ness of the ice they may be very easily overlooked." We make 

 these remarks with due reserve, not having yet seen the glaciers 

 referred to. 



The explanation just given has been brought to the test of 

 experiment. ABCD, fig. 10, is a wooden trough intended 

 roughly to represent the glacier of the Rhone, the space A C E F 

 being meant for the upper basin. Between E F and G H the 

 trough narrows and represents the precipitous gorge down which 

 the ice tumbles, while the wide space below represents the com- 

 paratively level valley below the fall, which is filled with the ice, 

 and constitutes the portion of the glacier seen by travellers de- 

 scending from the Grimsel or the Furka pass. A C L M is a 

 box with a sluice front, which can be raised so that the fine mud 

 within the box shall tlow regularly into the trough, as in the 



Fig. 10. 





cases already described. The disposition of the trough will be 

 manifest from the section, fig. 11. While the mud was in slow 

 motion downwards, a quantity of dark-coloured sand was sifted 

 over the space A C E F, so as to represent the debris irregularly 

 scattered over the corresponding surface of the glacier ; during 

 the passage of the mud over the brow at E F, and down the sub- 

 sequent slope, it was hacked irregularly, so as to represent the dis- 

 location of the ice in the glacier. Along the slope this hacking 

 produced an irregular and confused distribution of the sand; 

 but low(;r down, the patclics of dirt and the clean spaces between 

 them gradually assumed grace and symmetry; tliey were squeezed 



