

VOLCANOES OF THE INNER HEBRIDES. 317 



eruptions occurred in this land of the Inner Hebrides the whole 

 country appears to have been elevated out of the sea. The present 

 Duke of Argyll was the first to demonstrate the condition of the old 

 land by describing the section at Ardtun Head on the northern shore 

 of the Ross of Mull. There, near the base of the cliff, preserved in a 

 mud stream, formed by ruin washing down the fine volcanic ashes, 

 and afterwards sealed down by thick beds of basalt, are the leaves of 

 species of Platanus, and the large conifer Sequoia langsdorfii, which 

 occurs in the London Clay, and in the older tertiary deposits of Green- 

 land, Spitzbergen, Iceland, and Central Europe. 



In Ireland a more abundant flora has been described by Mr. W. 

 H. Baily, from volcanic-mud beds beneath the basalt at Ballipallidy. 

 The volcanic activity of this region probably extended over a pro- 

 longed period of time, for several leaf-beds in the island of Mull are 

 separated from each other by ashes, indicating that the eruptions were 

 intermittent, as they are in Etna and Vesuvius. 



The old volcanoes of the Inner Hebrides are now known from 

 nothing but skeletons of the cones. The loose ashes which formed the 

 upper parts of mountains have been worn away, or blown away, some- 

 times to the thickness of 5000 feet, and nothing remains where the 

 volcanoes stood but cores of granite or gabbro which formed the 

 matter erupted into the base or the throat of a volcano from which 

 the surrounding basalts or felstone lavas were ejected. 



The Mull Volcano. One of the most interesting of the skeleton 

 volcanoes forms the S.E. of the island of Mull. Previous to the out- 

 burst the Mull country was formed of Upper Cambrian Kocks like 

 those seen on the opposite coast of Morvern. Through these rocks, 

 granite of Primary age rises to form the south-west of the island. 

 And resting on the Cambrian Mica-schist, secondary rocks are seen 

 beneath the tertiary lavas at many places round the coast. 



Professor Judd 1 fixes the building of the old volcano as dating from 

 the Lower Tertiary period. The central mass consists of granite, but 

 all round the granite is the less crystalline rock called felsite, whicli 

 granite becomes when it cools rapidly. The altered rhyolites or felsites 

 are covered by beds of felsitic ashes and agglomerates ejected into the 

 air and subsequently consolidated by the action of rain. After a 

 period of activity of unknown duration the volcanic fires of Ben More 

 died away, and the volcano was probably denuded, so that most of 

 the ashes were washed away and the granites and felsites were 

 exposed on its surface. After this interval the volcanic fires broke 

 out again, but brought to the surface another kind of rock which 

 consolidated to form a central core of gabbro 2 or hypersthenite. 

 This gabbro burst through the granite and has sent sheets of fluid 

 rock into the granite in every direction, forming dykes. Ashes 

 were once more thrown out, and some of those basic agglomerates still 



1 Q. J. G. S., vol. xxx. 



2 The name gabbro is a convenient term which may be used in a generic 

 sense for this rock. There is no diallage in it, but it does not contain true 

 hypersthene. 



