Charlton, Blackheath, and Lewisham. April 30th, 1881 - Geologists' Association excursion
| From: A record of excursions made between 1860 and 1890. Edited by Thomas Vincent Holmes , F.G.S. and C. Davies Sherborn, F.G.S. London: Edward Stanford [For the Geologists’ Association], 1891. Source: Cornell University copy on the Internet Archive (Public domain work) |
Director—J. Logan Lobley, F.G.S. (Proc., Vol. vii. p. 142.)
After visiting the great pit at Charlton to see the junction of the chalk and tertiary beds, the party proceeded to the almost equally famous section at hanging-wood hill, displaying the woolwich shell-beds. The Upper and Lower Cyrena beds are very well developed and shells, in good condition, may be obtained in abundance. The shells are Cyrena cuneiformis, C. depredita, and C. cordata. The shell-beds also yield amongst other species the gasteropods Melania inquinata, and Cerithiunz funatum in considerable abundance, but the "Ostrea-bed" of the Ballast-pit section thins out at this place. Overlying the shell-beds we find the "Plant-bed," noticed by Dr. H. J. Johnston Lavis, in 1876 (Proc., vol. iv. p. 528) containing Dicotyledonous leaves and seed-vessels, but it is not nearly so well developed here as at Lewisham and at Bromley.
On reaching Blackheath, the party assembled around the shaft sunk for the purpose of investigating the cause of the subsidences which had occasioned so much anxiety and interest amongst the inhabitants of the neighbourhood. The first of these subsidences occurred after an unusually heavy fall of rain on April 12th, 1878; but this attracted little attention compared with that caused by two others, which took place in November, 1880. Almost circular openings in the Heath were formed, of a diameter of seven or eight feet, widening bell-shape fashion below, and having a depth of nearly twenty feet. Arrangements had been courteously made to afford every facility to the Geologists by Mr.. H. W. Jackson, the Hon. Secretary of the Lewisham and Blackheath Scientific Association, who were trying to explore one of these sinkings.[1] The probable causes of these subsidences were discussed at the pit's mouth by H. W. Jackson, J. Logan Lobley, and T. V. Holmes. Messrs. Jackson and Lobley were inclined to think , them due simply to hydro-geological influences, while Mr. Holmes thought these agents unable to produce these results unless aided by the existence of artificial cavities of the Denehole class; as the impeivious beds of the Woolwich series would otherwise prevent water that had fallen on the surface of Blackheath from getting lower than the base of the Blackheath Pebble-Beds.
From: Kent: Lewisham, Blackheath, and Charlton. [The sections at Lewisham and Charlton have generally been visited on the same day, and may therefore be conveniently grouped together here. The first excursion to Charlton took place on August 13th, 1860, and the report of its occurrence occupies four lines in the Proceedings (vol. i. p. 64). The first visit to Loampit Hill, Lewisham, was made in 1868, during the suspension of issue of the. Proceedings, while excursions were made to Charlton in 1866 and 1869, of which no report appeared. The Loampit Hill sections were inspected on May 7th, 1870 (Proc., vol. ii., p. 33), and again on April 25th, 1874, particulars of which follow.]
References
- ↑ The great expense attending the exploration obliged the Lewisham and Blackheath Scientific Association to leave off before any decisive results could be attained. A " Report of the Committee for the Exploration of the Subsidences on Blackheath " was published in 1881, drawn up by Mr. J. K. Laughton, M.A., Chairman. To the Report are appended some " Observations by T. V. Holmes, F.G.S.," with a geological section across Greenwich and Blackheath, and diagrams to illustrate the way in which—granting the existence of an artificial chamber in the Chalk, with a narrow shaft leading to it—a hollow would naturally be formed at the base of the Pebble Beds, resulting sooner or later in a subsidence. (See Figs. here reproduced).—(8vo, Blackheath, 30 pp.;see also Geol. Record, 1880-4, p. 496).