various parts of Scotland. 417 



pertain to the same system of rocks. Yet I have reason to suppose 

 that the beds of it which exist in the district of Aberfoyle, alternate 

 with a sort of intermediate rock, which I am incUned to consider as 

 the latest of the primitive, or the oldest of the transition series, a 

 rock approaching at least as near to the character of graywacke, as 

 to that of micaceous schist, if it be possible, as I suspect it is not, 

 to draw any line between these two classes of rocks. In this case, 

 the same limestone will, like clay slate, bear a share in both these 

 artificial divisions, for artificial I must needs consider divisions which 

 nature has separated by a boundary so feeble and so undefinable. 



Ails a. 



The craig of Allsa, from which the specimens now exliibited arc 

 taken, resembles the summit of a huge mountain rising abruptly out 

 of the deep. Such in fact it is, and not a mere rock, as its name 

 might induce one to suppose. It shelves rapidly into the sea, and 

 is surrounded by deep water on all sides except the south eastern, 

 where a small beach has been formed by the accumulation of its 

 ruins. I regret that the derangement of my barometer, a derange- 

 ment unfortunately too frequent, prevented me from ascertaining 

 its altitude ; but by comparing its appearance with that of Arthur's 

 seat, and computing from the time it required to ascend it, it cannot 

 be much less than 1000 feet in height. It is called 940 in some of 

 the sea charts, but on what authority I do not know. 



Its circumference cannot be less than two miles, and it therefore 

 forms a large island, which is covered with verdure, and is the 

 habitation of gulls, awks, gannets, goats and rabbits. Its shape is 

 round and cumbrous when viewed from the north-west, but whea 

 seen from the north it assumes an elegant conical figure. 



Vol. II. 3 g 



