24 THIRD LETTER ON GLACIERS. [1842. 



nearly uniform in the higher part ; this corresponds to the less 

 elongated form of the loops in the upper part of fig. 5. 4. In 

 the highest parts of such glaciers, as the curves become less 

 bent, the structure also vanishes. 5. In the wide saucer-shaped 

 glaciers already spoken of, which descend from mountain-slopes, 

 the velocity being, as in shallow rivers, nearly uniform across 

 their breadth, no vertical structure is developed. On the other 

 hand, the friction of the base determines an apparent stratifica- 

 tion, parallel to the slope down which they fall. 6. It also 

 follows immediately (assuming it as a fact very probable but 

 still to be proved, that the deepest part of the glacier moves 

 slower than the surface), that the frontal dip of the structural 

 planes of all glaciers diminishes towards their inferior extremity, 

 where it approaches 0, or even inclines outwards, since there 

 the whole pressure of the semifluid mass is unsustained by any 

 barrier, and the velocity varies (probably in a rapid progression) 

 with the distance from the soil ; whilst, nearer the origin of the 

 glacier, the frontal dip is great, because the mass of the glacier 

 forms a virtual barrier in advance ; and the structure is com- 

 paratively indistinct for the same reason that the transverse 

 structure is indistinct, viz., that the neighbouring horizontal 

 prisms of ice move with nearly a common velocity. 7. Where 

 two glaciers unite, it is a fact that the structure immediately 

 becomes more developed. This arises from the increased velo- 

 city, as well as friction of each, due to lateral compression. 

 8. The veined structure invariably tends to disappear when a 

 glacier becomes so crevassed as to lose horizontal cohesion, as 

 when it is divided into pyramidal masses. Now, this immediately 

 follows from our theory ; for so soon as lateral cohesion is de- 

 stroyed, any determinate inequality of motion ceases, each mass 

 moves singly, and the structure disappears very gradually. 



I might add more illustrations ; but let these suffice for the 

 present. It is not difficult to foresee, that, if my view should 

 prove correct, a theory of glaciers may be formed, which, with- 

 out coinciding either with that of Saussure or Charpentier, shall 

 yet have some thing in common with both. Whether that of 



