Canon Bonneij — Moraines and Mud-streams in the Alps. 15 



moraine could not do, for if, instead of forming a mound, it trailed 

 along after the retreating ice, it would be comparatively thin. 

 Some glacialists, however, may claim the deposit for ground 

 moraine, which once loomed very large in not a few imaginations, 

 and was defined as "rock rubbish derived from the subjacent 

 rock masses by the ice itself." Such material no doubt exists, 

 but to what extent (as I have repeatedly urged) must be deter- 

 mined by proof, not by hypothesis. Spitzbergen and Greenland 

 were then generally supposed to bear some resemblance to the 

 condition of the Alps in the Great Ice Age. But the researches of 

 Professors Gregory and Garwood in the former, and of Professor 

 Chamberlin with other American observers in the latter, have not 

 been rewarded by the discovery of enormous masses of indubitable 

 ground moraine, exactly resembling the Boulder-clay of Britain 

 and North Germany. Material to which the former term may be 

 applied seems to be produced in one of three ways : (1) in certain 

 cases an advancing glacier pushes before it, more or less levels 

 down, and finally travels, as if along a terrace, over what began 

 as terminal moraine ; (2) when a glacier ends in an ice-cliff, 

 fragments from the upper parts of this and rock debris from the 

 top may fall down, become frozen together, and then adhere to 

 the lower part of the advancing mass, by which they are carried 

 down the valley and finally deposited on its rocky floor, when the 

 ice melts away; (3) either this material, or any picked up locally 

 by the glacier as it is moving downwards, may be sometimes 

 distributed by differential movements of the ice in a more or less 

 stratified manner through its lower portion. This approaches 

 nearest to the old ideal of ground moraine ; but as that stratification 

 rarely extends for more than a hundred feet from the bottom of 

 the glacier, the material which it has left cannot be very thick.^ 

 But as an ice-sheet, when moving over nearly level ground, 

 seems not only to be incompetent to erode but even to override 

 loose material, already deposited, one layer, in case of a second 

 advance, might be superposed on another. In the Alps, however, 

 a retreat of the ice is generally signalized in the lower regions by 

 a deposit of stratified gravel, while in the upper the glaciers were 

 obviously able to keep their rock beds tolerably clean. We cannot, 

 therefore, in my opinion, apply this explanation to the deposits 

 under discussion. Morainic — that is, partly composed of ice-deposited 

 material — they may be,- but they are not true moraines. 



The Alps accordingly appear to have passed through a phase of 

 denudation which is still in process in the Himalayas. In the 

 former, when the snow and ice first disappeared from the zones 

 which are now uncovered for most of the year, the rock would be 

 not only rather thickly sprinkled with morainic debris, but also 



1 So far as I can judge from the excellent illustrations to the papers mentioned 

 above, the debris can hardly amount to one-fifth of the whole mass, so that the 

 former is seldom likely to exceed 20 feet, and -would generally be much less. 



- This, if I mistake not, is included by Continental writers in the term ' Glacial 

 Schotter.' 



