On the Blackheath pebble-bed, and on certain phaenomena in the geology of the neighbourhood of London / Sir Charles Lyell.

  • Lyell, Charles, Sir, 1797-1875.
Date:
[1852]
Catalogue details

Licence: Public Domain Mark

Credit: On the Blackheath pebble-bed, and on certain phaenomena in the geology of the neighbourhood of London / Sir Charles Lyell. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    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-liquifaction 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 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, micaschist and quartz rock, once called primitive, and once supposed to be of a date anterior to the creation of living beings, which nevertheless 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 nummulites of tlie overlying Bagshot sands were in ex- istence. 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 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 flints is considered by every geologist as the production of a modern era, when contrasted with the long series of antecedent rocks now known, each formed in succession when the globe wTas inhabited by peculiar assemblages of animals and plants long since extinct. [C. L.] In the Library were exhibited : — Fifty Febbles from Blackheath and Woolwich, collected by the late Major Bovs of Woolwich—Specimens of Gold Quartz, Sul- phuret of Mercury from California, and Topaz v'ith Mica, &c. [Exhibited by Mr. Tennant ] Bronze Cast of Napoleon, taken shortly before death — Judge Fraser’s Lion-spear — Caffre Instruments of War. [Exhibited by Ur. W. V. Pettigrew, M.R.I. &c.] Seaward’s Patent Brine-valve and Saline Detectors — and specimen