530 ISLE OF MAN. GEOLOGY. 



although very sparingly dispersed, in different parts of 

 the interior. Several modifications of hornblende schist, 

 and of argillaceous schist with distinctly imbedded crystals 

 of hornblende, occur also in similar situations. It is even 

 possible that the numerous substances, which are now 

 only to be seen on the shores where the tide washes them 

 up, are the remains of the general alluvial deposit, thus 

 brought from their submarine habitations, like the jaspers 

 and agates which abound on the eastern coasts of Scot- 

 land. The greatest variety of these rolled pebbles is 

 to be observed on the western shore, and they abound in 

 the vicinity of Peel. Jaspers of various colours, quartz, 

 porphyries, and granites, are the predominant substances. 

 Pebbles of chalcedony, similar to those formed in trap 

 rocks, are also to be seen, and these are collected by the 

 natives for the purposes of ornament. 



A VERY slight topographical sketch of the rocks which 

 form the Isle of Man, will be sufficient for the purpose 

 of preceding the geological details ; and, as they are dis- 

 posed in a very simple manner, these details will hereafter 

 be attended with little geographical confusion. 



The inspection of the coloured map will assist the reader 

 in comprehending their situations and general boundaries. 



Granite occurs in one situation in the immediate vicinity 

 of the Boon river, at a very short distance from the road 

 side, between Laxey and Ramsey. The quantity exposed 

 does not extend to many yards, and having been sub- 

 jected to the action of water, it is every where decom- 

 posed. It was also observed in Foxdale mine, when that 

 was formerly wrought, but there is now no opportunity of 

 ascertaining its existence. 



It will be readily perceived on inspection of the map, 

 that the principal part of the island is composed of schist^ 

 which occupies at least five-sixths of the surface. The 

 boundary of this rock, on the northern side, is the allu- 



