of Devonshire and Cornwall. 155 



tors seem to have undergone great changes by the lapse of tlme^ and 

 they were probably higher at a former period than they now are. 



The grauwacke covers the lower part of Carn Marth, and rises 

 exactly to the height of five hundred and forty-three feet, which is 

 about two-thirds of that of the mountain. 



According to the mean of nine barometrical observations, the height 

 of Redruth at Gray's Hotel, in the middle of the town, is four hun- 

 dred and fourteen feet above the level of the sea; about two hundred 

 paces beyond the first milestone from Redruth to Truro, the grau- 

 wacke disappears, and is superseded by a ridge of granite which 

 continues exactly to the end of the first mile ; there the land lowers, 

 and we re-enter the grauwacke, on which formation Scorrier House 

 stands.* 



Forth Towan is another place on the Bristol Channel, four miles 

 from Scorrier House, where the direction and inclination of the 

 strata of grauwacke may be well observed. The cliffs are high and 

 rather abrupt, and the rock has been very much excavated at the 

 bottom by the action of the waters. Quartz abounds in it. 



I observed that the grauwacke assumed a more slaty structure 

 as it approached the sea from Scorrier House. The sands at Forth 

 Towan extend pretty far into the interior of the country. 



St. Agnes's Beacon is an insulated eminence of a pyramidal form, 

 situated N.E. of Forth Towan, a short way in the interior ; it has 

 nearly the same degree of inclination on all sides, and is quite co- 

 vered with debris. It is entirely composed of grauwacke, though 

 six hundred and sixty-four feet above the level of the sea, and in 



* Scorrier House, on the road from Redruth to Truro, is three hundred and seventy- 

 seven feet above the level of the sea : it is a house, which mhieralogists who visit Corn- 

 wallj and who seek instruction as well as good company, ought not to fail to visit. 



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