880 



THE WONDERS OF GEOLOGY. Lect. VIII. 



of the south of Scotland ; and successively the principal 

 secondary groups of England. " In all," as Mr. Miller 

 observes, " there is an approximation to parallelism with 

 the Caledonian Valley, affording proof that this was the 

 general direction of the elevatory force, during all the im- 

 mensely-extended term of its operations, and along the entire 

 length of the Island."* 



41. Structure of Ben Nevis. — Though all granitic 

 rocks are of the same general character as to structure, 

 composition, and formation, they belong to different epochs; 

 and when in juxtaposition, or intercalated with sedimen- 

 tary beds, their relative age may be determined as we have 

 previously explained. Even when these aids are wanting, 

 different epochs of eruption are sometimes indicated, by 

 variations in the mineral aspect of the rocks ; and I will 

 conclude this subject with a short notice of a highly illus- 

 trative example. 



Ben Nevis, the monarch of the Scottish mountains, is 

 situated on the southern border of the great Caledonian 

 Valley, suddenly rising up in imposing grandeur from the 

 low country, to an altitude of 4,370 feet above the level of 

 the sea. The base and lower portion of the mountain are 

 composed of gneiss and mica-schist ; above and within which 

 is a zone of granite ; and within the latter, and rising out 

 of it, is a central, naked, rocky prism of porphyry, which 

 is the nucleus, and forms the highest peaks of the moun- 

 tain. 



The inference as to the relative age of these three dif- 

 ferent masses of plutonic rocks from their order of super- 

 position, is the very reverse of that deducible from such an 



* The Old Red-sandstone, p. 105. " It is a fact not unworthy of 

 remark, that the profound depths of Loch Ness were affected by the 

 great earthquake of Lisbon in 1755 (ante, p. 809) ; and that the impulse, 

 true to its ancient direction, drove the waves in long furrows to the 

 north-oast and south-west." — See Appendix, 1). 



