LOCALITIES OF GRANITE. 



63 



again in the Isle of Man, and in the counties of Dublin and Wicklow 

 in Ireland. Blocks of granite are found in the beds of some of the 

 rivers in the northwest part of Yorkshire, and in clay pits in Lanca- 

 shire and Cheshire, at a great distance from any granite mountains. 

 Most of the granitic rocks on Charnwood Forest are of that kind de- 

 nominated sienite.* Aniong the English localities of granite, I have 

 recently ascertained, that both granite and imperfect gneiss rise to the 

 surface near Bedworth in Warwickshire, evidently a continuation of 

 the Charnwood granite. 



Granite sometimes forms veins, shooting up into the superincum- 

 bent rocks. This is a fact of some geological importance, as it seems 

 to indicate, either that the granite has been in a state of fusion, the 

 heat of which has softened and rent the upper rocks, and forced up 

 the granite, in a melted state, into these fissures ; or else, that the 

 granite and the rocks resting immediately upon it were both in a flu- 

 id state at the same time, and are contemporaneous. A remarka- 

 ble instance of granitic veins in argillaceous schistus at Mousehole 

 in Cornwall is described in Dr. Thomson's Annals of Philosophy, 

 May, 1814. "The schistus is of a greyish colour, rather hard, but 

 breaks in large fragments in the direction of the strata. The gran- 

 ite is of a fine grain, and the felspar is of a light flesh colour, and 

 contains but a small portion of mica. At the junction, numerous 

 veins of granite may be traced, from the rock of granite into the 

 schist. Some of these veins may be observed upwards of fifty yards, 

 till they are lost in the sea, and in point of size, vary from a foot and 

 a half to less than an inch. It may deserve notice, that, as the fel- 

 spar is of a flesh colour, it is impossible for any observer to consid- 

 er them as quartz veins : one of these large veins is dislocated, and 

 heaved several feet by a cross course. Quartz and fragments of 

 schistus, having the appearance of veins, are found in the granite 

 veins. At one place there is a very curious and satisfactory phae- 

 nomenon. One of these veins of granite, after proceeding, vertical- 

 ly, some distance, suddenly forms an angle, and continues in a di- 

 rection nearly horizontal for several feet, with schistus both above 

 and below it. This appearance most completely destroys one of the 

 theories suggested for the explanation of similar veins at St. Michael's 

 Mount, viz. that a ridge of projecting granite had been left, and schis- 

 tus deposited afterwards on its sides." 



In 1816 I visited the place, which is close by the sea-side, at low 

 water, and observed some appearances which I believe have not hith- 



* According to Brogniart, granite, siente and porphyry, are frequently, observ- 

 ed, graduating into each other in some parts of France ; and he forms this conclu- 

 sion : "En etudiant les granites d'un grand nombre de pays pour tacher de disting- 

 uer clairment les anciens granites des nouveaux, on trouve presque peu de pays 

 granitiques, qu'on puisse rapporter avec certitude a cette ancienne et primitive 

 formation des granites." Jovrnal des. Mines, Mars, 1814. 



