120 REMARKS ON THE 



the trodden surface of the rock, an appearance very similar to 

 mica-slate, for which substance it might readily be mista- 

 ken, (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 ob- 

 served, that the above specimens are selected from the 

 most remote corners of the peninsula. On examination, I 

 think they will be found sufficiently similar to the Grauwacke 

 of Werner, to be entitled to be classed along with that rock. 

 Dr Berger, in his paper on the physical structure of Cornwall, 

 gives them no other name, and if authority is to be qualified 

 by experience, the opinion of one who has traced the footsteps 

 of Saussure, and who has studied the geognosy of Werner 

 with the utmost enthusiasm, cannot fail to be received with re- 

 spect. 



I have thus endeavoured to shew by the selection of spe- 

 cimens, and by the opinion of a very scientific observer, that 

 the stratified rock of Cornwall is grauwacke. It would be un- 

 candid, however, not to acknowledge, that the general texture 

 of this rock was different from the grauwacke of the south of 

 Scotland ; it was more of the slaty variety, and frequently seem- 

 ed, from its smooth and soft feel, to contain a large proportion 

 of magnesian earth *. 



I understand, in a course of lectures now delivering, a very 

 material alteration has been proposed upon the Wernerian Sys- 

 tem, 



* Since I read this paper, I have had occasion to pass through the transition 

 country of Peeblesshire, &c. On former occasions, I was in the habit of search- 

 ing lor characteristic specimens of the grauwacke ; I now looked for such as re- 

 sembled the killas of Cornwall, which I found in abundance, (Nos. 62, 63.). 



