INDEX. 475 



PAGE 



Trap, of Trotternish, the alter on only apparent, and this 

 is probably the case in all other instances of such supposed 

 alternation ....... 



, columnar on a large scale 



, generally composed of augit and felspar 



Trees, found in the marsh lands near London 

 Tunnel of the Tavistock canal, description of the . 



, accuracy in the direction of the 



drift, its length and ventilation while making 

 Tweed, account of the beds on the banks of the 

 Trotternish in Sky, its rocks described 



181 

 181 

 182 

 302 

 146 



155 

 90 



178 



Veins, numerous and chiefly of porphyry traverse the slate of 



Cruachan 118 — 121 



of trap sometimes occur in the slate of Cruachan 118 — 123 



' of Huel Peever described by Mr. Williams . . 139 



of copper and tin run from north-east to south-west . 148 



that do not run north-east and south-west, generally un- 

 productive of metal and seem of newer formation . 148 



occur but in few sorts of rocks ..... 151 



run through all the strata . . . . . . 151 



at Morwel Down, their dip ..... 151 



, general notice of such as are productive near Morwel 



Down ......... 152 



, filled by infiltration 395 



, porphyritic. See Porphyritic veins 



Vegetable remains in chalcedony, Dr. Mac Culloch on . 398 

 Ventilation of the drift for the Tunnel of the Tavistock canal, 



reference to account of 155 



Warburton, Henry, Esq. Note on Magnesian breccia . 205 



On some beds of Shell-marle in Scotland 305 



Whernside, height of . 435 



Williams, John, Junr. Esq. Account of some remarkable distur- 

 bances in the veins of Huel Peever in Cornwall . 139 



