GIBB OYSTER CONGLOMERATE BED AT BROMLEY. 325 



interesting localitiea he was acquainted with. At and around Bromley 

 is an area of some extent, formed by the Lower London Tertiaries ; a 

 small patch of chalk, however, crops out to the east of the town, in 

 which are some ancient quarries. One of these possesses some interest 

 from being underground, and containing, as I was informed, several 

 intricate windings. 



The London clay, with the underlying plastic or "Woolwich clays, and 

 Thanet sands, constitute the lower division of the Eocene strata of the 

 Tertiary group of rocks. The London clay extends over several counties 

 of England, constituting a large part of the soil of Essex, nearly the 

 whole of Middlesex, and portions of Berkshire, Surrey, and Kent.* In 

 the last two counties it more especially occupies the northern parts. The 

 plastic or mottled clays and sands which underlie the London clay are 

 seen in the Isle of Wight in contact with the chalk, or in the London 

 basin at Reading, at Blackheath, "Woolwich, and Bromley. These clays 

 and sands have been well described by Mr. Prestwich, and termed by 

 him the " "Woolwich and Eeading Series," and the Thanet sands of the 

 Lower London Tertiaries. However much the other divisions of the 

 Eocene strata may have differed in their mineral character in the 

 deposits of England and Paris, Sir Charles Lyell has well observed that 

 there is an exception to the general rule in the plastic and mottled clays 

 of this lower division of the Eocene series ; for whether it is studied in 

 the basins of London, Hampshire, or Paris, we recognise everywhere 

 the same mineral character. This uniformity of aspect must be seen 

 in order to be fully appreciated, since the beds consist simply of sand, 

 mottled clays, and well-rolled flint pebbles derived from the chalk, and 

 varying in size from that of a pea to an egg."f 



These characters are presented by an examination of the oyster-bed 

 ' near Bromley, which consists of a series of thin layers of sand and 

 , pebbles, and an extensive deposit of oyster and other shells. In some 

 [ parts the latter have formed with the pebbles and sand a distinct con- 

 i glomerate, several inches thick, the cementing medium being calcareous, 

 and apparently derived from the shells themselves. This conglomerate 

 has been extensively quarried at one time, and even now many of the 

 houses, grottos, and garden- walls in Bromley are built with the rock 

 thus ornamented with the shells, which are so naturally grouped 



* Geology of England and Wales, by Conybeare and Phillips, 

 t " Manual of Elementary Geology," p. 221, Fifth Edition. 



