in the (leology of the Neighbourhood of London. 97 



the same foldings and contortions as the underlying cretaceous and 

 oolitic strata. 



Sir Charles Lyell next proceeded to shew 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 some- 

 times of the contraction of rock, or of the semi-liquefaction or com- 

 plete 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 re- 

 garded as the outward sign of much greater internal revolutions tak- 

 ing place simultaneously far below. Even the precise nature of the 

 changes in the texture of rocks produced by subterranean 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 intense. 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 ante- 

 rior to the creation of living beings, which nevertheless were sedimen- 

 tary 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 nummulites 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 

 probably as widely separated from the era 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 era. Nevertheless the white Chalk 

 itself, with its hints, is considered by every geologist as the produc- 

 tion of a modern era, when contrasted with the long series of ante- 

 cedent rocks now known, each formed in succession when the globe 

 was inhabited by peculiar assemblages of animals and plants long 

 since extinct. 



VOL. MIL NO. CV. — JULY 1852. G 



