94 Mr H. M. Stoker on the China-stone and 



The bed from which it is obtained is about three-fourths 

 of a mile in extent, on the contiguous borders of the parishes 

 of St Dennis and St Stephens, occupying almost the centre 

 of the central granite district of the county, and is sur- 

 rounded by other primary rocks of igneous origin, which, as 

 they stretch towards the coast on either side, merge into 

 beds of killas or clay-slate. On the eastern and northern 

 boundaries, the granite is more irregular and abrupt in cha- 

 racter than on the other sides, is more porphyritic, and con- 

 tains a much larger proportion of felspar, in large white or 

 red opaque, cubic, or rhomboidal crystals ; while on the 

 south it is separated from the neighbouring granite by a 

 large elvan dyke. And it is worthy of notice, that, while on 

 one side of this you may find China-stone perfectly pure, on 

 the other, only from one to two feet distant, the stone is 

 rendered useless by the presence of small plates of talc im- 

 bedded in dense gray granite, which also forms a portion of 

 the eastern boundary. 



Any one who has carefully studied the porphyry dykes, or the 

 general nature of the primary rocks of our county, cannot but 

 have noticed the difference in the temperature at which some 

 of them have been upheaved, compared to that of others ; for 

 while some of our granites are composed of substances which 

 have in their crystals a certain amount of water that has not 

 been lost, others have no trace of it, their felspar having 

 become an amorphous-looking powder (kaolin) ; and others 

 presenting the same waxy edge on fracture that is noticed in 

 porcelain, particularly the elvan dykes : and from this it has" 

 been conjectured, though tome it appears doubtful, that as the 

 melting point of other minerals was considerably below that 

 of these rocks, at the time of the extraordinary convulsion to 

 which our county has been subjected, the China-stone was 

 by this means freed from iron, &c. ; and that, on its having 

 reached the surface, the water by which it was surrounded 

 at once caused the crystals of felspar to split, lose their out- 

 line and character, and become easily acted on by the solvent 

 power of rain-water, which, by depriving it of a portion of 

 its potash, leaves the crystals of quartz or silicic acid and 

 plates of mica, glistening with a silvery hue, imbedded in a 



