Observations on Glaciers. 351 



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

 shaped glaciers already spoken of, which descend from moun- 

 tain-slopes, the velocity being, as in shallow rivers, nearly uni- 

 form across their breadth,, no vertical structure is developed. 



On the other hand, the friction of tlie base determines an 

 apparent stratification, 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 froti- 

 tal dip of the structural planes of all glaciers diminishes to- 

 wards 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 ve- 

 locity varies (probably in a rapid progression) with the dis- 

 tance 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 compara- 

 tively indistinct for the same reason that the transverse struc- 

 ture 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 be- 

 comes 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 imme- 

 diately follows from our theory ; for so soon as lateral cohesion 

 is destroyed, any determinate inequality of motion ceases, each 

 mass moves singly, and the structure disappears very gradu- 

 ally. 



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

 present. It is not difticult 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 M. Rendu may not avail something, I am unable to 

 say, not yet having been able to procure his work. 

 - It yet remains to decide, what is the cause of the succession 

 oi' dirt-bands at considerable distances on the surface of the 



