STAFFA. GENERAL DESCRIPTION. 



nature of this columnar range intelligible, it is necessary 

 to commence the description at its western extremity, 

 which is situated above Mackinnon's cave. 



The whole face is here divided into three distinct 

 beds of trap of different characters ; the lowest con- 

 sisting of that conglomerate called trap tuff, the next, 

 of the great columnar range, and the uppermost of an 

 irregular mixture of small implicated and bent columns 

 with an amorphous basalt. These beds dip towards 

 the east; that dip being most sensible and most easily 

 determined in the lowest or conglomerate stratum, because 

 its upper surface is nearly straight. The angle of in- 

 clination with the horizon is nine degrees, as nearly 

 as I could determine it in a turbulent sea. The 

 thickness of the conglomerate at the western side, 

 at about a quarter ebb, is fifty feet; necessarily dimi- 

 nishing as the bed extends eastward, until it reaches 

 a point intermediate between the great cave and the 

 boat cave, where it disappears under the water. It 

 has been said that a bed of sandstone lies below this 

 conglomerate. That is certainly possible, but no such 

 rock is to be seen at the low water of an equinoctial 

 spring tide, one of the periods at which I visited the 

 island. I imagine that incautious observers have mistaken 

 the basaltic conglomerate for a sandstone. This mistake 

 may readily be made at a distance ; since, independently 

 of the smooth surface of the rock, it is thickly covered 

 with the common Lepas, which gives it a grey colour 

 very like that of white sandstones in similar situations. 

 It presents one among a thousand examples, of the caution 

 required in pronouncing on the nature of a rock from 

 any thing short of close examination. 



Next in order is the columnar bed, the chief source 

 of the beauty and interest of Staffa. This follows the 

 inclination of the conglomerate, but not regularly, since 

 it is not parallel throughout; the upper surface being 

 uneven. Hence the columns vary in length along the 



