INTRODUCTION XXXIX 



pallescens is to be found. South of Newbury, in ponds, Mentha Pulegmm 

 occurs along with Ranunculus hederaceus ; at the base of the Wargrave 

 outlier is a marshy spot which gives a home for Carex paniculata, &c. 

 On the sandy portions of the beds sand-loving plants are necessarily 

 to be found ; in such situations Filago apiculaia, Erigeron acre, Trifoliwn 

 arvense, T. striatum, Hieracium boreale, H. sciu2)hiliim, &c. occur. Perhaps, 

 however, the more interesting flora is to be found on the ' drift 

 gravels ' coAering the Reading Beds, on which grow many rare and 

 interesting plants. Among such species are Potentilla argentea, Trifolium 

 scabrimi, T. striatum, T. subterraneum, T. arvense, Dianthus Armeria, Jasione, 

 Anthemis nohilis, Erythraea pulchella, &c. 



The London Clay is a thick mass of clay, of a bluish or greyish 

 colour, but weathering brown on the surface, very uniform in its 

 character throughout its whole thickness (which in some places is as 

 much as 400 feet) and over its whole range. It contains bauds of 

 septarian nodules of clayey limestone. At its base is a peculiar bed 

 known as the * Basement Bed,' which consists of rounded flint pebbles 

 embedded in green and yellow sand, locally cemented by carbonate of 

 limestone into hard tabular slabs. 



The outcrop of the London Clay in Berkshire is a broad one. The 

 range of hills from Cold Ash Common to Mare's Ridges consists 

 greatly of this formation, and there are two brickyards in it in the 

 district west of Englefield, Near Frilsham is another outlier, in which 

 the Basement Bed is exposed to the west of Frilsham House. On the 

 large ovitlier at Tilehurst the deposit is 100 feet thick. Near Newbury, 

 at the Shaw brickyards, a good section is exposed. 



North of the Kennet there are several outliers of London Clay, 

 among them a small piece resting on the Wickham outlier of the 

 Reading Beds ; others occur on the same beds at Snelsmore, Oare, 

 Yattendon, and on a large area of Bucklebury Common, where the 

 clay is much obscured by drift gravels. South of the Kennet the 

 London Clay is more continuous, especially along the southern slope 

 of the Kennet valley from Crookham nearly to Reading. The large 

 and interesting area about Burghfield, Mortimer, Shinfield, Swallow- 

 field, &c., and the country immediately bordering the Emborne stream, 

 is of the same foimation, but a great proportion of its surface on the 

 south of the Kennet is concealed either by the over-lying Lower 

 Bagshot Beds, or by drift gravel which is deeply spi-ead over its 

 surface in many places. The London Clay occupies a wide area 

 between Reading and Windsor. The country is often flat, but the 

 well-marked range of hills on the south near Binfield, Winkfield, 

 Warfield, and Snow Hill in Windsor Great Park, belong to the same 

 formation. On the Chalk between Wargrave and Maidenhead are 

 some interesting outliers of the Tertiary group ; these have their base 



