formed by Ancient Glaciers. 349 



the air near the lateral edges of the glacier, caused by radia- 

 tion from the neighbouring rocks, occasions a more copious 

 melting of the ice and snow in those parts, and consequently 

 a greater quantity of water is introduced into what remains 

 unmelted. This water being refrozen at night, produces a 

 greater expansion near the edges than in the central portions 

 of the glacier ; and this excess accelerates the motion of the 

 sides downwards. It must be recollected that a glacier is not 

 one solid piece of ice, but is broken up and intersected by 

 many chasms or fissures of greater or less width and depth, 

 which allow an independent motion of its different parts. 

 This greater expansion has a tendency also to divert the de- 

 scending stones from a rectilinear course, and to carry them 

 toward the point of least resistance, in other words, nearer 

 to the sides ; so that a large portion of them, instead of reach- 

 ing the foot of the glacier, are deposited in longitudinal or 

 irregularly curved lines on the inclined slopes of the contigu- 

 ous rocks, their peculiar form being modified by local circum- 

 stances. It is also evident that the greatest accumulations of 

 these lateral shelves, or morains, will be found near and upon 

 the most prominent slopes of rock, especially on the side next 

 to the head of the glacier; because these projections not only 

 arrest the stones in their downward course, but by their 

 agency in causing more radiation, melting and freezing, at- 

 tract, if I may so say, a greater quantity of surface wreck. 

 Again, as the opposite sides of a glacier at any given point 

 have a general coincidence of level, these morains will often 

 be found to correspond in horizontal position ; though, for 

 obvious reasons, not so precisely as the opposite shores of a 

 bay or lake. They must also be formed solely of fragments 

 from the higher surrounding rocks, not rounded into pebbles, 

 but more or less angular, or mixed with clay or earth, in pro- 

 portion to the nature and hardness of the material. Neither 

 sea nor freshwater shells will be found among them. Other 

 morains are formed at the foot of the glacier, and often pre- 

 sent very different appearances ; but as it is to the lateral 

 ones that most of the terraces on the Galashiels hills are to be 

 referred, I shall not pursue the explanation further. 



I think a careful perusal of the details given in my former 

 paper will show that a large portion of these terraces, or 

 rather shelves, correspond with the morains whose origin I 

 have just been tracing. Their broken and interrupted cha- 

 racter on the Eastern Eildon and on Williamlaw ; their irre- 

 gular width and rude horizontality of surface, combined with 

 a general coincidence of level ; their angular stones and the 

 total absence of gravel, sand or shells, are precisely such as 



