86 Mr. J. Ball on the Formation oj 



gorges, is to me a conclusive proof that some agency other than 

 that of ice must have directed the original formation of valleys 

 of this type. In one respect the inequalities of the sides of 

 alpine valleys offer a stronger argument against their glacial 

 origin than those of their bed. The surface of the ice, even near 

 the side of the glacier, moves much faster than the part in con- 

 tact with its bed ; and it suffices to cut away the foundation of a 

 lofty cliff at the point where the glacier abuts against its base, to 

 determine its fall. Looking at the operation as a whole, it is to 

 me quite inconceivable that a glacier should be competent to 

 scoop out valleys a mile or more in depth, and yet be unable to 

 remove the mam inequalities from its own channel. 



A comparison of the effects of existing glaciers with those of 

 the present torrents must lead many observers besides Professor 

 Tyndall to the conclusion that the former are far more powerful 

 excavators than the latter, but do not to my mind justify the 

 inference that no assignable limit can be placed to the work 

 which they have actually accomplished. Vast as the period 

 may be during which glaciers occupied many of the valleys of 

 the Alps, it was not long enough to enable them to accomplish 

 more than a certain definite amount of excavation ; and I think 

 it likely that the amount may hereafter be determined with some 

 degree of accuracy. Indications are not wanting both of what 

 glaciers have achieved, and of what they have failed to achieve. 

 Ever since the range of Mont Blanc assumed its present form, 

 before the so-called glacial epoch, and during that long period, 

 and ever since down to the present hour, the snow that accumu- 

 lates in the basin of the Mer de Glace has been discharged into 

 the valley of Chamouni by the ice-fall of the Glacier des Bois. 

 During the whole of that immense period, the uttermost mecha- 

 nical effect of the glacier upon its bed has been applied to grind 

 down the ledge over which it has to flow, and to bring the chan- 

 nel to a uniform slope. It is impossible to doubt that a consi- 

 derable effect has been produced ; the ledge has been lowered 

 perhaps by 1000 feet, possibly more; the angle which the slope 

 of the ice-fall makes with the glacier above has been rendered 

 much more obtuse; but still the ice-fall remains, and the bed of 

 the glacier has not been ground down to the uniform slope. 



I refer to a well-known glacier, familiar to many readers, 

 though I can conceive a partial, but, I think, an insufficient 

 answer to my argument, founded on local conditions, and not on 

 general grounds. I could easily cite many similar instances 

 which would be less open to cavil. The same argument, mutatis 

 mutandis, might be applied to lateral obstacles, such as the rocks 

 known as P Angle on the west side of the same glacier. 



It is impossible to leave this part of the subject without some 



