ISLE OF MAN. GEOLOCV. SCHIST. 545 



In now reverting to the original question, namely, 

 whether the beds of schist bore any relation to the 

 exterior forms of the mountains, and whether their irre- 

 gularities have determined the disposition of the group, 

 it is evident that no light can be thrown on the subject, 

 unless future observers shall determine, throughout the 

 mountains, that disposition of the beds which eluded 

 my examination. The laminar tendency is obviously 

 incapable of furnishing any unexceptionable evidence 

 on this subject. Yet the preceding discussion will not, 

 imperfect as it is, be without its use, since it will point 

 out some of the causes which prevent the solution of 

 similar questions in other cases, and excite useful doubts 

 whether, in many instances, general conclusions to this 

 effect have not been founded on imperfect views of the 

 nature and bearings of the schistose rocks. 



As it is in vain to endeavour to convey an idea of 

 the varieties of rocks by description, I shall content 

 myself with a very superficial notice of the principal 

 modifications of schist occurring in the Isle of Man ; 

 enumerating rather their leading features than at- 

 tempting to describe individual specimens. Such as are 

 applicable to useful purposes, have been already suffi- 

 ciently pointed out in the topographical part of this 

 article. 



The clay slate appears frequently in its simplest form, 

 as a soft fissile uniform substance, of different colours, 

 passing from a greyish white through various darker 

 tints to lead blue, and ultimately to an imperfect black. 

 In certain cases it possesses a silky appearance, ap- 

 proaching at times to a plumbaginous lustre ; and, these 

 appearances by degrees increasing, it assumes the aspect 

 of a fine micaceous, and of a talcy slate. In structure, 

 it is occasionally fibrous, and this variety predominates 

 at the southern end of the island, while in other cases 

 it shows neither fibrous nor foliated tendency. It is 

 proper to remark that these varieties are found indif- 



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