114 Dr.BE-RGER on the physical Structure 



In Cornwall, as in the Hartz, the covering of grauwacke never 

 rises very high, and we find that here, the more elevated points, 

 although their absolute height be not very considerable, are left bare. 



Here also, as in other countries,* the two varieties of grauwacke are 

 uniformly found connected with one another : they in general cover 

 the transition limestone, whereas secondary greenstone and clay- 

 slate occur in it in subordinate beds, and perhaps the formations of 

 serpentine, of diallage with felspar, and of talcose slate, of which I 

 shall afterwards speak, are similarly situated. 



Though the cliffs at Stonehouse are of limestone, nevertheless 

 Mount Edgecumbe, which is only separated from them by the 

 Hamoaze, belongs to the grauwacke formation. We here find that 

 rock passing from the state of a coarse argillaceous sandstone, of a 

 reddish colour, not effervescing, and stained by oxide of iron, to that 

 of a fine-grained grauwacke-slate, with red veins, giving it the ap- 

 pearance of ribbon jasper. It occurs in strata, dipping S.S.E. at an 

 angle of about 65° or 70% which is nearly the same as that of the 

 limestone cliffs of Plymouth harbour. The stratification is best seen 

 on the south side of Mount Edgecumbe about half way up ; and 

 especially from the great terrace to the arch^ and beyond that on 

 the way to the zig-zag walk. At the top of the hill the grauwacke 

 becomes less distinctly stratified, and begins to separate into rhom- 

 boidal pieces. Maker Heights,! Rame Head, Higher Blarick in 



appeared to him like that of Plymouth : he added, that it had been excavated in some 

 places by the sea, and that the fissures had since been filled up with a gravelly conglome 

 rate. 



* Brochant, Traite de Mineralogie, tome ii. p. 5S8. 



+ The altitude of this place, computed from the Trigonometrical Surrey, is four hun- 

 dred and two feet above the lerel of the sea. 



