REMNANTS OF EXTINCT VOLCANOES. 457 



formation is raised in some places about 500 feet above the sea 

 and pierced with basaltic dykes. The famous upheaval of the 

 Snowdon range with its basaltic columns and recent shells in 

 deposits 1,350 feet above the sea. The coalfield of South Wales 

 with its north and south faults and fissures, and some apparently 

 modern dykes of basalt ; and, again, the recentl}^ discovered 

 basaltic columns a little west of Tavistock, in Devon, from thence 

 to Padstow, North Cornwall — between the two places basaltic 

 dykes and sheets being very abundant ; and lastly the well- 

 known micaceous trap that extends from near Newquay on the 

 north to the Lizard on the south. The whole of this chain of 

 evidence will, I think, prove the connection to be complete from 

 the Western Islands of Scotland to the Wolf Eock off the south- 

 west coast of Cornwall. The volcanic forces which had during 

 the long Mesozoic period deserted our part of the earth's surface, 

 appear to have returned to it in full vigour in the Tertiary epoch. 

 "In the newer Paleozoic periods, the direction of the great 

 volcanic band which traversed our islands appears to have been 

 from north-east to south-west ; but in Tertiary times a new set 

 of fissures were opened, running from north to south, [which 

 intersected those of earlier date, ] and the intensity of its activity 

 gradually increased till it attained its maximum in the Miocene 

 period, when a great chain of volcanic mountains stretched north 

 and south along the line of the inner Hebrides, the north-east 

 of Ireland and the sea which separates Grreat Britain from 

 Ireland, as far as the British Islands are concerned."* 



It there appears to have ceased, or there is apparently no 

 further notice taken of these grand phenomena, but I claim 

 their extension southward to the Lizard and the Wolf rock, and 

 believe that I can produce reasonable evidence to confirm this 

 claim by a great number of slides of the south-western rocks, 

 and many hand specimens, from which many of the microscopic 

 sections were taken ; the map, too, shews the non-conformity 

 and disparity of these rocks, when compared with the older 

 rocks, consisting of clay slate, fragmentary conglomerate, and 

 limestone, the latter being replete with remnants of marine 

 organisms, dipping at an angle of 48° SS.E., beneath the newer 



* Judd, volcanoes, p. 278. 



