572 ISLE OF MAN. GEOLOGY. TRAP VEINS. 



phyry ; the fallacy being only detected by penetrating to 

 a considerable depth in the stone. This case is parallel to 

 those formerly noticed in treating of the Slate isles. 



Some of the veins also possess the amygdaloidal cha- 

 racter, the compact greenstone basis being filled with 

 rounded grains, which, as far as I observed them, 

 seemed always to consist of calcareous carbonate ; and in 

 certain cases the porphyritic and amygdaloidal characters 

 are combined in the same rock. 



At Pool vash, the trap veins are of an earthy character 

 and very pale grey colour, not much unlike some of 

 the tufaceous rocks which so often accompany the great 

 deposits of trap. Even in these cases, certain parts of the 

 vein assume the more ordinary character of greenstone. 

 All these are very firmly united to the limestone which 

 they traverse, and contain grains of pyrites interspersed 

 throughout. In many places, .they possess a foliated or 

 schistose structure, which is detected by the progress of 

 decomposition ; the whole exfoliating in thin earthy 

 laminae, the direction of which is always parallel to the 

 side of the vein. 



The last variety which remains to be described, is 

 remarkable for containing olivin dispersed in considerable 

 abundance throughout it, in small grains, and of a yellow 

 colour. This variety is also schistose, and is found at 

 Scarlet point. 



Before closing the account of the rocks of this island, it 

 is necessary to point out one substance, which, although 

 it may be viewed as incidental, is nevertheless interesting ; 

 since it serves to throw light on the composition of certain 

 mineral veins which have been the subjects of discussion, 

 and may also perhaps explain an appearance occur- 

 ring in Lewis, which was noticed in the account of that 

 island. 



Near the point where the schist and sandstone unite, in 

 the neighbourhood of Peel, a conglomerate of rolled 

 pebbles is seen adhering to the face of the schist, which 



