Ch. VIII.] THE GRANITIC AND SCHISTOSE ROCKS. 153 



not improbable; and it is not unlikely that this spot might 

 have been temporarily obscured by shingle or debris from 

 the cliff, when they visited it ; but at present the appearance 

 does not agree with their sketch. The granite laid down as 

 the main mass, is an irregular portion of the vein ; and slate, 

 at the surface, intervenes between it and the granite. 



This junction so well displays the granite-veins, and is so 

 easy of access, that, before concluding the details of these 

 phenomena in Cornwall, we think it desirable to give a 

 minute description of this important example ; which may be 

 rendered more intelligible by the accompanying sketch. 



The main mass of granite (occupying the left-hand corner 

 of the annexed plan) runs in a north-westerly direction to- 

 wards the village of Paul, forming the hill immediately west- 

 ward of the shore at this place. It is porphyritic, and, at a 

 distance from the junction, large grained; but adjoining 

 thereto, the basis, in which the large crystals are imbedded, 

 generally varies from fine-grained to an uniform texture, as 

 in the felspar porphyries. The irregular patches of granite, 

 situated between the southern vein and the main mass, have 

 the same composition : some of these patches are evidently por- 

 tions of the subjacent mass laid bare by the abrasion of the 

 waves, for several parts of their surface are still covered by 

 persistent laminae of slate ; whether they are all so, remains 

 to be ascertained. The several granite-veins, for the most 

 part, consist of compact felspar; which, in some places, is 

 very quartzose, but seldom porphyritic. The large northern 

 vein or elvan, however, often abounds in crystals of felspar. 

 The slate at the junction, or immediately adjoining the 

 granite- veins, is compact, hard, and finely granular, or crys- 

 talline and quartzose. Both the granite and the slate, as 

 already observed, are traversed by fissures or joints parallel 

 with the granite and quartz -veins, which intersect the mass at 

 right angles. Sometimes these lines correspond with the 

 point of junction, but very often they pass indifferently 

 through either rock ; and, in these cases, the slate and 



