Excursion to Riddlesdown and Croydon. April 17th, 1875 - 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)

Directors: Caleb Evans, F.G.S., and J. Logan lobley, F.G.S. (Proc. Vol. iv. p. 282.) Leaving the train at Caterham Junction Station members had but a few yards to walk to the fine section of the Upper Chalk at the western extremity of Riddlesdown. Gradually ascending the Down, while proceeding eastward, the members attained an elevation which enabled them to obtain fine views of a portion of the Chalk country, with its gently swelling hills and riverless valleys, formed by the denudation of the North Downs.

On reaching the mouth of the half-made tunnel of the abandoned Surrey and Sussex Railway the geologists immediately entered the excavation, and examined the Chalk there exposed with its nodular and tabular flint. Mr. Caleb Evans, who has, from his observations of the various Chalk sections of this neighbourhood, obtained sufficient evidence to enable him to divide the Chalk into palaeontological zones, explained that the beds here exposed are the Upper Kenley beds, containing an assemblage of fossils markedly different from the fauna of the Purley beds, higher in the series, and also from that of the immediately underlying Lower Kenley beds. While Inoceramus Cuvieri is wanting in the Upper Kenley beds, it is present in both the Purley beds and the Lower Kenley beds. Holaster planus and Micraster cor-bovis occur in the Lower Kenley beds, but are not found in the Upper, which appear to be characterised by the abundance of three of the best-known of Chalk species, Micraster cor-anguinum. Echinocorys scutatus (olim Ananchytes ovatus), and Spondylus spinosus.

In his paper "On some Sections of Chalk between Croydon and Oxted " (8vo, London, Geol. Assoc., 1870), Mr. Evans fully describes this and other sections exposed during the formation of the railway; and the following list of species from the Upper Kenley beds of this locality is given:

PROTOZOA	BRACHIOPODA
Cephalites campanulatus, Smith.	Terebratula cornea, Sow.
Brachiolites convolutus, Smith.	Terebratula semiglobosa, Sow
ECHINODERMATA	Rhynchonella limbata, Schl.
Echinocorys scutatus, Leske.	Rhynchonella Mantelliana, Sow.
Micraster cor-anguinum, Gmelin.	Crania Ignabergensis, Retz.
Cidaris vesiculosa, Goldf.	LAMELLIBRANCHIATA
POLYZOA	Peden quinquecostatus, Sow.
Desmeopora semicyindrica, Rœm	Spondylus spinosus, Sow.
Flustra	PISCES
Hornera or Homæosolen.	Lamna.

The summit of the Down was then crossed, and following a lane the party struck the London and Brighton road at the picturesque grove called "Purley Oaks," near to which is the Chalk quarry in which was found a granite boulder, possibly deposited on the bed of the old Chalk sea by an iceberg from the ice-capped lands of the Cretaceous epoch [or dropped from the roots of a drifting tree.]

A mile walk brought the members to the outskirts of Croydon, where the Cretaceous rocks give place to the Tertiaries of the London Basin, the southern edge of which is here found. Near to the conspicuous tower of the Croydon Waterworks, a large excavation affords a good exposure of the junction of the Chalk with the overlying Thanet Sands. This was the last section visited, and the party then took train to London.