462 CANNA. DESTRUCTION OF ROCKS. 



tunity of extending the observations so far as to decide 

 to what kinds of rock it belongs or to which it may 

 possibly be limited. I may however enumerate those 

 places where it is to be seen. 



It is very conspicuous in the island of Staffa, where 

 the excess of waste in the parts exposed to the atmosphere 

 only, above that where the action of sea and air alter- 

 nate, is strongly marked by the columnar causeway which 

 in many places extends so far beyond the vertical face of 

 the island. 



I have pointed out a similar appearance in Rum, in the 

 platform which extends from Harris to the point of Bri- 

 dianoch; and it is also to be seen, although in a less 

 marked manner, on the southern shores of Egg, as well 

 as in many parts of Mull and Sky which it is unnecessary 

 to enumerate. In all the cases here quoted, the rocks 

 are of trap or syenite, but the circumstance is by no 

 means limited to these. 



A long range of secondary rocks has been described as 

 extending from Portree to the northern end of Sky, and 

 the same has been shown to exist on the eastern side of 

 Rasay. In both these instances, the strata being nearly 

 horizontal, and the cliffs decomposing so as to present 

 mural faces, the effect is equally remarkable as in Canna 

 or Rum where a similar mode of wasting prevails. The 

 strata, whether of sandstone, shale, or limestone, are here 

 found projecting far beyond the cliffs in the form of flat 

 shores, never rising above the high water mark; while 

 the surface of the uppermost stratum, whatever that may 

 chance to be, appears to resist all efforts towards waste ; 

 at least for a comparatively long time. A similar dura- 

 bility under the same circumstances is found in the gry- 

 phite limestone of Sky and of the adjacent islands; 

 although the effect is less conspicuous in consequence 

 of the inferior altitude of the land. The result in these 

 cases is seen in the long extended reefs and foul shores 

 which render this coast so dangerous to vessels engaging 



