ISLE OF MAN. GEOLOGY. 531 



vial tract already described. On every other, with the 

 two exceptions which will presently be stated, it termi- 

 nates in the sea? This mass of schist presents several 

 varieties, and is in many instances applied to economical 

 purposes. These I shall here state ; referring to a distinct 

 place, the account of its geological relations and mine- 

 ralogical characters. 



It is every where obvious that the more tender 

 varieties are in a state of rapid decomposition, and that 

 they are converted, in the last stage of this process, into 

 the clay which forms the leading division of the agricul- 

 tural soil of the island. These clays differ in aspect and 

 composition ; as do the rocks whence they are derived ; 

 their colour varying in proportion to the quantity of iron 

 contained in the original rock, and according to the degree 

 of change that metal has undergone during the progress 

 of decomposition : their ingredients also differ more or 

 less, as quartz, mica, or calcareous earth, have taken a part 

 in their formation. Hence the several soils resulting from 

 them vary materially; more however to the experience 

 of the agriculturist than to the eye of the mineralogist. 



Fissile slate is not very abundant among these rocks, 

 but it appears in different places. It has been wrought 

 at Balla gawn, in the neighbourhood of Peel, and pos- 

 sibly in other situations which did not fall under my 

 inspection. In many places, and among others at Laxey, 

 the fissile varieties are thick, and excellently adapted for 

 the purpose of flags ; containing much quartz, and bearing 

 a considerable resemblance to those which are found in 

 Isla at the places where the quartz rock and the clay slate 

 approach each other. The size of such flag slate, when 

 in its native place, is sometimes enormous ; large plates 

 of twenty or thirty feet in dimensions, or even more, 

 being visible in many parts of the island. No attempt 

 is however made to raise these entire ; there being 

 no demand for specimens so large. They are generally 



