TRANSITION ROCKS. 119 



of Devon and Cornwall. In mentioning grauwacke, which he 

 distinguishes from grauwacke-slate only by its compactness, 

 he says, " It is found higher up than the grauwacke-slate, it 

 " may be supposed to have been precipitated more slowly, and 

 " under less powerful pressure ; whereby the mass has been al- 

 " lowed to contract, and to assume a kind of crystallization. It 

 " rests immediately on granite." Tlie conclusions he draws are 

 different from mine ; but from the above quotation it appears, 

 that the circumstance I observed at Teign Bridge is usual in 

 similar situations all over Cornwall. 



Near St Austle, on the road leading to Carclaze mine, I 



found grauwacke, (No. 23.) in my opinion extremely well cha- 

 racterised ; also on the road to Cambourn, not far from Dol- 

 coath, (No. 31.) ; likewise on the shore near Penzance (No. 

 42, 43.). Here it is also fine-grained, and tough under the 

 hammer, and at no great distance from granite. Near Oak- 

 hampton, I found it along with grauwacke-slate, in the most 

 unequivocal state, (No. 57.) ; and on the shores of the Bristol 

 Channel, near Ilfracombe, the rocks are all of the same mate- 

 rial *. 



Here, on the beach, to the west of the town, I spent some 

 hours the evening before I crossed to Swansea ; and found no- 

 thing among the rocks, to lead me for a moment to question, 

 that they were wholly composed of grauwacke. Indeed I even 

 remarked some of the contortions which are so common in this 

 rock. Next morning, however, when walking down to the 

 boat, imder a point where a small battery is built, I found on 



the 



* The specimens alluded to, were examined by the gentlemen present when 

 this paper was read, who considered those from the road leading to Carclaze 

 mine, and from near Oakhampton, as Grauwacke ; and those from the vicinity of 

 Penzance as Greenstone. 



