306 Clmrles Maclaren, Esq.. on the 



the importance of those glaciers, and calculated the inclination of the 

 line connecting them with Jura, which is as follows : — 



Minutes. In feet. 

 From Plan-y-Beuf to Chasseron (p to/), 22' 1 foot in 156 



... St Bernard to Chasseron (t r to /), 40' 1 ... 86 



The data, however, on which these calculations rest are open to 

 some objections. When the glacial traces consist of polished rocks, 

 which are seldom continuous over great spaces, it may happen that 

 the highest have escaped notice. Thus M. de Beaumont puts down 

 2300 metres as the upper limit near the G-rimsel Pass ; but Agassiz 

 and Desor subsequently found polished rocks on the mountain which 

 forms the western side of that Pass, the Siedelhorn, at 2447 metres 

 of elevation (Desor " Excursions et Sejours" p. 242.) Thus 482 

 feet were added to the difference of level between r and /, and the 

 general slope was raised from 1 foot in 160 to 1 foot in 153. Again, 

 when the difference of level between the traces at Brieg and Mar- 

 tigny (b and d), a distance of fifty miles, was put down at 70 metres 

 or 229 feet, should not some allowance be made for the effect of the 

 great glaciers which descended from the lateral valleys of Saas, St 

 Nicholas, Annivier, and Erin (at n and y), in enlarging the princi- 

 pal glacier and forcing it to expand upward at points below Brieg. 

 In the next place, glacial traces may once have existed at a greater 

 elevation, and been subsequently obliterated. None are marked in 

 M. de Beaumont's table as occurring in that long space of fifty miles, 

 but as the rocks on both sides are of limestone, which wastes rapidly, 

 few polished or striated surfaces could be expected. Moraines, in- 

 deed, may exist, though they also are liable to obliteration. On the 

 whole, we cannot be sure that the traces now visible at any locality 

 are the highest which have existed. 



■iumoiu 

 Depth of the Ancient Glacier. ^X^ 



The enormous depth of the ancient glaciers is still more astonish- 

 ing than their length or breadth, and to this element we can approxi- 

 mate with the aid of Keller's map, which gives the height not only 

 of the mountain tops, but of sundry points in the bottom of the 

 valleys. Thus the elevation of the upper limit of erratics at Aernen 

 (between r and b) is 1813 metres above the sea, in the table, and 

 that of the town standing at the bottom of the valley, according to 

 Keller's map, is 2990 French feet. Converting the measures into 

 our own, and deducting the latter from the former, the depth of the 

 glacier is found to be 2756 English feet. The whole calculated in 

 this way are as follow : — 



- 



