of Devonshire and Cornwall 115 



White-sand Bay, the point where my excursion to this part of the 

 coast ended, and precisely in the meridian of the Eddystone Ught-^ 

 house, all belong to the grauwacke formation. In White-sand Bay- 

 this rock, forming the cliffs, separates by very regular rhomboidal 

 joints. It is of a whitish colour, of a friable texture, like that of the 

 gres-molasse, and might pass for a corneous trap in a state of de- 

 composition. It is accompanied by a rock, having a reddish argilla- 

 ceous base, containing much oxyd of iron, and fragments of compact 

 limestone, and which effervesces with acids. 



There is at Peter Point in St. John's Creek, very near Torr Point, 

 a bed of greenstone, in the composition of which there is a good 

 deal of steatite, completely included in the grauwacke. Though of 

 small extent, it is quarried for building. Not far from this place, 

 on the banks of Lyhner Creek, and on the estate of Sir Henry 

 Carew, there is another bed of greenstone : it is immediately adjoin-,- 

 ing the ferry. This bed extends from one bank to the other ; and 

 on the right or south side of the creek there is a large quarry of it. 

 Very remarkable differences may be observed in the texture of the 

 greenstone, though the specimens be taken from the same bed. The 

 base is sometimes so close, so homogeneous, that single unconnected 

 specimens of it might pass for corneous trap* with pyrites dispersed 

 through it : other specimens, however, taken quite close to the pre- 

 ceding, are of a composition and grain, between that of corneous trap 

 and greenstone : these are in my opinion sufficient reasons for com- 

 prehending all the varieties of this substance, under the common 

 denomination of greenstone. 



* It is, more properly speaking, what the German mineralogists call graustpin (grey- 

 stone) which they describe as having nearly a homogeneous base, of an ash-grey 

 colour, and of a dry aspect. Brochant, Traite de Miiieralogie, torn. ii. p. 608. 



p 2 



