On Staffa. 447 



There is a soil of considerable depth on the surface, and it is 

 covered with herbage. 



It is aimofct superfluous to say that the whole island consists 

 of a mass of basalt. I have indeed been told, that a sandstone 

 bed has been seen at low water on the southwestern side, but I 

 had not an opportunity of observing it. This is the part of the 

 island, where, if in any place, it should, from the inclination of 

 the strata, be perceived; and there is no reason to doubt the as- 

 sertion, as we find most of the trap rocks of the Western Islands 

 lying on beds of sandstone. Is is equally superfluous to describe 

 the basalt, since specimens of it are in every one's possession. 

 It may be sufficient to remark, that itfs texture is more compact, 

 more crystalline, and less earthy than that of basalt in general, 

 and that it is at the same time less homogeneous, less black, 

 more fragile, and more sonorous. But it would be idle to at- 

 tempt to apply different terms to the endless varieties of the rocks 

 of this tribe. 



This basalt exhibits two modifications : the columnar, so often 

 described, and the amorphous, which is generally more or les* 

 amygdaloidal, containing imbedded zeolites of different sorts. 

 I saw no examples of basaltic breccia, or of trap tuff, as it is im- 

 properly called. 



It is in the amorphous basalt that the zeolites are most abun- 

 dant. The nodules vary from the size of a pea to that of a 

 hen's eg<^ and upwards, and generally exhibit specimens of ra- 

 diated mesotype and of analcime. The cubical zeolites (cha- 

 basite) are of rare occurrence, and the mesotype is seldom gia- 

 uular, and never, as far as I saw, capillary. The lamellar variety 

 of stilbite is occasionally found filling the intervals of approximate 

 columns. I did not observe any zeolites in the larger and more 

 perfect columns, but in the smaller and more irregular ones they 

 occur, though rarely. 



If we were to view the island only from the southwestern side, 

 and at half tide, we should conclude that it has been formed of 

 three distinct deposits, or beds of basalt. Of these the lower- 

 most appears in some places amorphous, but it is not easy to see 

 enough of it to judge whether it actually forms a continuous bed. 

 It is only from the analogy of Canna, and the other basaltic 

 islands of this sea, that we should be tempted to generalize this 

 conclusion. 



The next bed is that which is divided into those large co- 

 lunms which form the most conspicuous featore of Staffa, and it 

 varies from 30 to 50 feet in thickness. The upper one appears 

 at tt distance to be an uniform mass of amorphous basalt ; but on. 

 A nearer inspection it is found to consist of small columns, laid 

 and entangled in every possible direction, often horizontal, and 



generally 



