91 8 HARRY FIELDING REID 



condition would be satisfied if the motion were everywhere 

 parallel to the glacier's bed, but we have already seen that on 

 account of the pressure from behind there is really a small 

 movement of the ice away from the bed. Above the neve-line 

 this is reversed. Here there is accumulation ; and, unless the 

 reservoir continually increases in thickness, the motion must 

 have a component downward into the glacier, and this com- 

 ponent must be greater where the accumulation is greater, i. e., 

 in general as we ascend the reservoir. We can thus draw on the 

 surface of the glacier the approximate directions of motion, and 

 beginning at the neve-line, where, as there is neither melting nor 

 accumulation, the motion must be parallel to the surface, we can 

 connect these lines and have a diagram of the lines of flow in 

 the whole body of the glacier (Fig. 2). The slight melting of 

 the glacier in contact with its bed would produce a small com- 

 ponent of the motion towards the bottom, and in the dissipator 

 also towards the sides ; but in the reservoir the accumulation 

 results in a movement away from the sides. In picturing to 

 ourselves the relative velocities of points at different distances 

 from the surface, it is best to consider points lying in a section 

 drawn everywhere at right angles to the lines of flow. The 

 velocity of points in such a section will diminish as we 

 approach the glacier's bed, on account of the friction which 

 acts on the ice there. We can also show the positions 

 assumed by the strata of annual accumulations. Perhaps the 

 best way to do this is to follow the successive positions of a 

 chosen stratum. At the end of the summer the snow deposited 

 during the previous year will end in a thin wedge at the 

 neve-line, and its thickness will at every point equal the cor- 

 responding annual accumulation. A year later the end of this 

 stratum, with but small loss by melting, will have been carried a 

 short distance down the surface of the glacier ; and every point of 

 the stratum following its proper line of flow, will have progressed 

 down the valley and into the body of the glacier, and the stratum 

 will have reached the position 2. Continuing in the same way 

 we can trace in a general way the position the stratum will have 



