176 Reviews- — On Ice as a Geological Agent. 



moraines x and y ; for lower down part of the material may disappear 

 by falling into crevasses. The same must be done for the moraines 

 6 and c, or for each of the medial moraines ; and also, in several 

 places, for the lateral moraines d and e. Then ascertain the rates of 

 the onward movement of the glacier, according to circumstances, in 

 various portions of its length, and at various seasons of the year; 

 and by these means will be ascertained to a great extent (but not 

 precisely) the quantity of matter carried annually on the surface of 

 the glacier to its termination, and this matter will represent a very 

 large part of the waste of the sides of the mountains that bound the 

 snow and glacier basins o, jp, q, and the sides of the mountains that 

 bound the glacier lower down towards its terminal moraine. 



3rd. The chief part of the remainder of the rocky and earthy 

 matter that is carried from the mountains to the level of the glacier, 

 will pass under it at its sides, and mingle with the material that finds 

 its way to the bottom of the glacier by means of crevasses and 

 moulins, and also with that which is the product of the erosive 

 action of the glacier exerted on its bed, and on the stone blocks 

 imprisoned at the bottom of the ice, A small part of the above- 

 named remainder may also be caught in the ice, and imprisoned in 

 rejoined crevasses. 



4th. We see no way of precisely estimating the amount of erosion 

 produced by the weight and movement of the glacier — that is to 

 say, the rate at which any given glacier may deepen and widen its 

 valley by pure wearing action, owing to the circumstances that the 

 sediments discharged along with the water that flows from the end 

 of a glacier do not represent the amount produced by mere erosive 

 force, for the reason stated under head 3. But it is essential to the 

 main question that correct estimate should be made of the amount of 

 solid matter brought from under the glacier by the help of running 

 water, and also of the amount carried away by the continual wasting 

 of streams of the terminal moraine. 



As regards the matter in suspension in the river, and also that 

 forced along its bottom, it should be estimated, if possible, at a 

 point r, just below where various streams unite that flow from the 

 ends of most great glaciers. Where there is only one stream (as in 

 the Aletsch glacier), the closer the better. The operation would 

 be very laborious ; for, unless frost and snow prevented it, it would 

 require to be done for every day in a year or years, and several 

 times each day, at least in summer and autumn, and probably in 

 spring and winter also. For example, in summer the quantity of 

 water varies largely, according to the heat of various periods of the 

 day ; and it would probably be necessary to make an observation 

 every day before sunrise, another some time before noon, another 

 between four and six o'clock in the afternoon, and another after 

 nightfall ; in fact sufficiently often to obtain an average for each day 

 in the year. 



With regard to the transport of heavier matter from the terminal 

 moraine (which forms a portion of this part of the subject) by 

 means of the estimates indicated under head 2, assuming that all 



