20 STAFFA. GEOLOGY. 



from that of the Giant's Causeway. It becomes of a 

 rusty brown on weathering, but decomposes no further. 

 It is this dark brown hue, seldom enlivened by the 

 growth of a lichen, but oftener blackened by the 

 dripping of water, that produces the sombre tone of 

 colouring which is the chief defect of Staffa as a 

 picturesque object. The yellow stain given by the 

 Lichen parietinus to some parts of the upper stratum, 

 is scarcely sufficient to relieve this uniform darkness; 

 nor does this substance form with it a happy combi- 

 nation of local colour. 



The amorphous basalt found in various parts of the 

 island, is precisely of the same texture with the co- 

 lumnar ; and contains in various places amygdaloidal 

 cavities, which are however most abundant in the soft 

 or tufaceous varieties. 



The zeolites are chiefly situated in this latter rock ; 

 yet they occur, although very rarely, in the solid, and 

 even in the columnar basalt. They are seldom re- 

 markable either for their size or beauty ; being far 

 inferior in both those respects to the specimens found 

 in the other basaltic islands of this country. These 

 nodules consist either of analcime or mesotype ; and 

 are more commonly solid than crystallized. In one 

 place I observed specimens of that substance which 

 is formed into concentric and radiated spheres, and of 

 which some foreign varieties have been distinguished 

 by the name of natrolite. Stilbite is more rare, and 

 appears chiefly to be disposed in very thin veins oc- 

 cupying fissures in the basalt; in which situation also 

 is found the little calcareous spar that occurs in the 

 rocks of this island. 



The last extraneous substance, if it may so be con- 

 sidered, is the basalt of those veins by which the 

 fundamental rock is traversed ; a circumstance from 

 which no part of these islands, whether basaltic or not, 

 seems to be exempted. They are not numerous nor 

 of very large size. The largest is found in the lowermost 



