246 ON GLACIERS IN GENERAL. 



ish bands on the glacier, the curves pointing downwards, and 

 the two branches mingling indiscriminately with the (lateral) 

 moraines, presenting an appearance of waves some hundred feet 

 apart, and having, opposite to the Montanvert, the form which 

 I have attempted to show upon the map,* where they are repre- 

 sented in the exact figure and number in which they occur. . . 



I was satisfied, from the general knowledge which I 



then had of the ' veined structure ' of the ice, that these coloured 

 bands probably followed that direction." t Farther examination 

 confirmed this conjecture, and showed that these superficial dis- 

 coloration s in the form of excessively elongated hyperbolas are 

 due to the recurrence (at intervals of some hundred feet along 

 the course of the glacier) of portions of ice in which the veined 

 structure is more energetically developed than elsewhere, and 

 where, by the decomposition of the softer laminae, portions of 

 sand and dirt become entangled in the superficial ice, and give 

 rise to the phenomena of dirt-bands, which thus at a distance 

 display (though in a manner requiring some attention to discover) 

 the exact course of this singular structure on the surface of the 

 glacier. The annexed figure 26 displays the superficial form of 

 the dirt-bands, and the course of the structural laminae projected 



fig. 26. Fig. 27. Mg. 28. 



horizontally. Fig. 27 shows an ideal transverse section of 

 the glacier ; and Fig. 28 another vertical section parallel to its 

 length. These three sections in rectangular planes will serve 

 to give a correct idea of the course of this remarkable structure 

 within the ice, but a more popular conception will be formed of 

 it from the imaginary sections of a canal-shaped glacier in the 

 annexed woodcut, Fig. 29. The structure of the compound gla- 

 cier, originally double, becomes gradually single ; and the frontal 



* Map of the Mer de Glace of Chamouni, etc., in Forbes s Travels in the Alps, 

 or in the Tour of Mont Blanc, etc. 



f Travels in the Alps of Savoy, etc., 2d edit., p. 162. 



