Ancient Extent of the Glaciers of Chamonix, 65 



The blocks detached from mountains are sometimes of gigan- 

 ' tic dimensions, some are found 20 metres in length, and such 

 as measure 10 metres in every direction are not rare in the 

 Alps. 



If the glacier were immoveable, these debris would remain 

 fixed in it without any order, but its movement causes a 

 certain arrangement in the distribution of these materials, 

 which shews a very remarkable degree of regularity. These 

 blocks are disposed on the glacier in long tracks parallel to 

 its sides, or they accumulate at the extremity in the form 

 of large transverse mounds. Both of these accumulations 

 have been distinguished by the name of moraines. 



The following is the mechanism employed in the formation 

 of moraines. The debris of the surrounding mountains falling 

 on the sides of the glacier, they share in its motion, and ad- 

 vance along with it ; but, additional quantities of materials 

 falling upon it, it may be said daily, are deposited in a line 

 with the first, and the whole united form those long con- 

 voys of substances which lie along the two sides of the glacier; 

 these are the lateral moraines, A glacier often presents many 

 lateral moraines, because the debris from above fall at points 

 unequally distant from the centre, and the degree of their 

 motion is consequently different. The greater part of tourists 

 who have visited the great glaciers of Switzerland are ac- 

 quainted with these lateral moraines, and more than one of 

 them can recall the fatigue they had to undergo before they 

 could scale these accumulations of gigantic blocks. They 

 might be called ramparts raised by giants to prevent access 

 to these fields of eternal snow, where nature has concealed 

 the secret of the last revolutions of our globe. After pass- 

 ing the lateral moraine, the traveller almost always discovers 

 a mound still more considerable, disposed longitudinally to- 

 wards the centre of the glacier, and which is named the 

 median moraine. This results from the junction of two glaciers 

 of nearly equal magnitude. At the extremity of the projec- 

 tion which separates them, the left lateral moraine of the 

 one rests against the back of the right lateral moraine of the 

 other. These two lateral moraines are soon confounded in 

 one, and form the median moraine of the new glacier, itself 



VOL. XUII. NO. LXXXV. — JULY 1847. E 



