Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/485

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475
INDEX.
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Trap, of Trotternish, the alternation only apparent, and this is probably the case in all other instances of such supposed alternation 181
──────────────, columnar on a large scale 181
──────────────, generally composed of augit and felspar 182
Trees, found in the marsh lands near London 302
Tunnel of the Tavistock canal, description of the 146
─────────────────────, accuracy in the direction of the drift, its length and ventilation while making 155
Tweed, account of the beds on the banks of the 90
Trotternish in Sky, its rocks described 178
Veins, numerous and chiefly of porphyry traverse the slate of Cruachan 118-121
──── of trap sometimes occur in the slatc 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 unproductive 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
William, John, Junr. Esq. Account of some remarkable disturbances in the veins of Huel Peever in Cornwall 139