476 Royal Institution. 



portions of the Swiss Alps of 8000 or even 10,000 feet, and enters 

 into the structure and composition even of the central axis of the 

 Alps, having been subject to the same movements and partaking of 

 the same foldings and contortions as the underlying cretaceous and 

 oolitic strata. 



Sir Charles Lyell next proceeded to show that a great series of 

 volcanic eruptions had occurred in Europe since the older Eocene 

 strata of the neighbourhood of London were deposited. Not only 

 Vesuvius and Somma as well as Etna and the extinct volcanoes of 

 Southern Sicily, but the trachytic and basaltic eruptions of the ex- 

 tinct volcanoes of central France are more modern than the London 

 Clay. The evidence consists not only of the superposition of igneous 

 rocks several thousand feet thick, to lacustrine strata of the middle 

 and upper Eocene periods, but also to the absence in the pebble- beds 

 constituting the base of the tertiary series of Auvergne, Cantal, and 

 Velay of any pebbles of volcanic origin. 



The Lecturer concluded by stating that the formation of every 

 mountain chain and every elevation and depression of land bears 

 witness to internal changes at various depths in the earth's crust. 

 The alteration has consisted sometimes of the expansion, and 

 sometimes of the contraction of rock, or of the semi-liquefaction 

 or complete fusion of stony masses and their injection into rents of 

 the fractured crust occasionally manifested by the escape of lava 

 at the surface. Every permanent alteration therefore of level may 

 be regarded as the outward sign of much greater internal revo- 

 lutions taking place simultaneously far below. Even the precise 

 nature of the changes in the texture of rocks produced by subterra- 

 nean heat and other plutonic influences since the commencement of 

 the Eocene period can be detected in a few spots, especially in the 

 central axis of the Alps, where the disturbing agency had been in- 

 tense. The table might be covered with specimens of gneiss, mica- 

 schist and quartz rock, once called primitive, and once supposed to 

 be of a date anterior to the creation of living beings, which never- 

 theless were sedimentary strata of the Eocene period which assumed 

 their crystalline form after the flints of Blackheath were rolled into 

 shingle, and even after the shells of the London Clay and the num- 

 mulites of the overlying Bagshot sands were in existence. 



Yet however remote may be the antiquity of the Blackheath pebble- 

 bed as demonstrated by the vast amount of subsequent change in 

 physical geography, in the internal structure of the earth's crust and 

 in the revolutions in organic life since experienced, its origin is pro- 

 bably as widely separated from the sera of the Chalk as from our own 

 times. For the fossils of the Chalk differ as much from those of the 

 oldest tertiary strata near London, as do the last from the organic 

 beings of the present aera. Nevertheless the white Chalk itself with 

 its flints is considered by every geologist as the production of a 

 modern aera, when contrasted with the long series of antecedent rocks 

 now known, each formed in succession when the globe was inhabited 

 by peculiar assemblages of animals and plants long since extinct. 



