PLUTONIC OR IGNEOUS ROCKS. 



647 



Aiguille de Dru. 



The external forms of granitic rocks are 

 very various, much depending upon their 

 texture, and consequent capacity to resist 

 decomposition from atmospheric agencies. Some of 

 yielding material are tame and uninteresting, having 

 been rounded by the disintegrating action of the air and 

 rains, as in Ben Lomond and other parts of the Grampians 

 in Scotland ; but others of a harder quality protrude in wild and rugged amorphous masses, 

 as in Aberdeenshire ; or in grand serrated structures, forming picturesque pyramidal peaks 

 rising into spires, as in the Isle of Arran and at Mont Blanc. The serrate or notched struc- 

 ture originated the application of the word sierra to mountains of that shape. The elon- 

 gation of notches into spires is finely displayed by the aiguilles around the monarch of 

 Switzerland, particularly the Aiguille de Dru, a singular granitic construction, the most 

 striking object, next to the glaciers, in the valley of Chamouni ; for the eye cannot embrace 

 the huge dimensions of " sovran Blanc." The aiguille is apparently isolated, and reaches 

 the height of eleven thousand feet above the level of the sea, the upper part forming one 

 continuous shaft of more than four thousand feet, gradually tapering to a point, of course 

 perfectly inaccessible. The sides are rounded, and are said to have a polish or glazing 

 like that which is sometimes on granite rocks exposed to the action of the sea ; " but 

 this," observes Mr. Bakewell, " I could not discern with my telescope. It appeared com- 

 posed of perpendicular plates of granite. By what means it has been shaped into its 

 present form it is difficult to conceive. When approaching the Glacier de Bois, it is impos- 

 sible to view without astonishment this isolated pinnacle of granite, shooting up into the 

 sky to such an amazing height. I have neither seen nor have I heard of any pinnacle of 



