2e Remarks on the Transition Rocks of Werner. 
wacke, and yet internally it was different. I had not pro- 
ceeded many paces, however, when J came upon granite, 
(No. 8.) the proximity of which, as before mentioned, is 
always marked by a very material alteration in the con- 
sistence of the adjoining rock. This alteration, I observe, 
was not unnoticed by Dr. Berger, in his interesting paper* 
on the physical structure of Devon and Cornwall. In 
mentioning grauwacke, which he distinguishes from grau- 
wacke-slate only by its compactness, he says, ‘It is-found 
higher ap than the granwacke-slate, it may be supposed ta 
have been precipitated more slowly, and under less power- 
ful pressure; whereby the mass has been allowed to con- 
tract, and to assume a kind of crystallization. It rests im- 
mediately on granite.” The conclusions ‘he draws are dif 
ferent from mine; but from the above quotation it appears, 
that the circumstance f observed at Teign Bridge is usual 
in similar situations all over Cornwall. 
ear St. Austle, on the road leading to Carclaze mine, I 
found grauwacke, (No. 23,) in my opinion extremely well 
characterized ; also on the road to Cambourn, not far from 
Dolcoath, (No. 31.) 3 likewise on the shore near Penzance 
(No. 42, 43.). Here it is also fine-grained, and tough un- 
der the hammer, and at no great distance from granite. 
Near Oakhampton, 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 material f. 
Here, on the beach, to the west of the town, I spent 
some hours the evening hefore I crossed to Swansea; and 
found nothing among the rocks, to lead me for a moment 
to question taal they were wholly composed of grauwacke. 
Indeed | even remarked some of the contortions which are 
so comman in this rock, Next morning, however, when 
walking down to the boat, under a point where a small 
battery is built, | found on the trodden surface of the rock, 
ab appearance very similar to mica-slate, for which sub- 
stance it might readily be mistaken (No. 61, 62.) ; but this 
resemblance appears to be owing to the friction of the feet, 
and the action of the weather, on a variety of grauwacke 
containing an unusual proportion of mica. 
By casting an eye over the map of Cornwall, it will be 
observed, that the above specimens are selected from the 
* Geological Transactions, vol.i. p. 112. 
+ The specimens alluded to were examined by the gentlemen present 
when this paper was read, who considered those frei the road leading to. 
Carclaze mine, and from near Oakhampton, as grquwacke; and those from 
the vicinity of Penzance as greenstone, 
most 
