Professor Forbes on the Leading Phenomena of Glaciers, 237 



cause, such as the melting of a coating of snow by a sudden 

 thaw, as in the end of September 1842, produces the same 

 effect as great heat would do. Also, whatever cause accele-, 

 rates the movement of the centre of the ice increases the differ- 

 ence of central and lateral motion. 



7he Veined Structure of the Ice is a consequence of the 

 Viscous Theory, 



We have now to complete what was partly said in Chapter 

 VIII., where we endeavoured to illustrate the phenomena of 

 the veined or ribboned structure of the ice, and to explain its 

 cause. 



This structure we have seen to consist in the recurrence of 

 alternations of blue and white, or compact and aerated ice in 

 a glacier, resembling the veins in chalcedony, the parts being 

 thin and delicately subdivided. 



We have found that this structure has all the appearance 

 of being due to the formation of fissures in the aerated ice or 

 consolidated neve, which fissures having been filled with water 

 drained from the glacier, and frozen during winter, have pro- 

 duced the compact blue bands. 



We have farther found that this ribboned structure fol- 

 lows a very peculiar course in the interior of the ice, of which 

 the general type is the appearance of a succession of oval 

 waves on the surface, passing into hyperbolas with the greater 

 axis directed along the glacier. That this structure is also 

 developed throughout the thickness of a glacier, as well as 

 from the centre to the side, and that the structural surfaces 

 are twisted round in such a manner that thd frontal dip, as we 

 have called it, of the veins, as exhibited on a vertical plane cut- 

 ting the axis of a glacier 

 occurs at a small angle 

 at its lower extremity, 

 and increases rapidly as 

 we advance towards the 

 origin of the glacier, as shewn in the accompanying figure. 



VOL. XXXV. NO. LXX. OCTOBER 1843. R 



