A RAMBLE THROUGH CATERHAM VALLEY. 135 



a mile or two of Gravel and Alluvium, until at 

 New Cross we met with the London Clay, which 

 extends as far as Croydon. Soon after Croydon 

 was passed, a momentary glimpse was had of the 

 Woolwich and Reading Beds, the lowest members 

 of the Tertiaries. These are made up of sand, 

 pebbles, and clay, and are brought to light in a 

 quarry by the railway side. Then immediately 

 came the chalk, cropping out in all its glory, and 

 forming the most conspicuous geological feature in 

 and around Caterham. The extreme boundaries of 

 the Tertiaries may be observed in many places where 

 the chalk is being quarried as, for instance, near 

 Caterham Junction ; for on the face of the chalk 

 occur sandy patches or outliers, which are really 

 portions of the Eocene deposits that by the pro- 

 cesses of denudation have become almost discon- 

 nected, in many cases quite so, from the main masses 

 of the Tertiaries. In times long gone by how long 

 who shall say ? the sand and gravel were deposited 

 in crevices in the chalk. Then in process of time, 

 as both sand and chalk were worn down, the thicker 

 portions of the Tertiary deposits in the chalk hollows 

 became separated from the principal part of the 

 same formation, being left as Tertiary islands in a 

 sea of chalk. If then the chalk be quarried at 

 right angles to these sandy courses, their fades will 

 seem to be surrounded by the chalk, and so will 

 present the appearance of patches or pipes, as can 

 be seen at Caterham Junction. 



This is not the only evidence that the Tertiaries 

 once extended farther south than they do now. 



