INTRODUCTION XXvil 



The Geological formations that come to the surface within the 

 county are shown in descending order in the following table : — 



Post Tertiarv -f ^^^^P^^ficial deposits including Clay with Flints. 



\ Low-level AlluviiTm. High-level Alluvium and Gravels. 



Tertiary ) f Bagshot Beds. 



or r Eocene - London Clay. 



Caenozoic -' ^ Reading Beds. 



( Chalk. 

 . Cketaceods -. LTpper Greensand. 

 Secondai-y ^ Gault. 



or , Neocomian Lower Greensand. 



Mesozoic I , Portland Beds. 



i Jurassic -' Kimeridge Clay \ 

 Coral] lan Beds. 

 V Oxford Clay. 



The general strike of the beds is nearly east and west, and the dip 

 is to the south ; so that, in travelling from north to south, we pass 

 continually on to higher and higher beds. The outcrops of the several 

 formations show on the map as a series of approximately parallel strips 

 crossing the county from west to east. 



The Oxford Clay consists of bluish or grey clay, which weathers to 

 a yellow or brown colour at the surface. It is probably not less than 

 500 feet thick in Berkshire ; in the upper jiart the bedding is in- 

 distinct, and the clay has a tendency to be lumpy ; the lower part is 

 more finely laminated and shaly. Large Septaria and thin beds of 

 earthy limestone occur in it. Selenite and Pyrites are common, and 

 the fossils are often pyritized. The country where the Oxford Clay 

 forms the surface is for the most part low-lying, flat, or feebly undu- 

 lating, and of unattractive aspect. Its soil is stiff, damp, and cold ; 

 and the land is usually under pasture. It is sparsely populated and 

 almost destittite of villages : one main cause of this is the difficulty of 

 obtaining a supply of water from the formation. 



In Berkshire the Oxford Clay forms a narrow strip of low-lying 

 land, a mile or two across, bordering the southern bank of the Thames 

 from Lechlade to Botley. It also stretches from Coleshill to Lechlade, 

 and the village of North Hinksey is situated on it ; a narrow strip 

 runs round Wytham Hill, and an irregular piece reaches as far south 

 as Iffley. Harrowden Hill near Longworth, situated on this formation, 

 is capped with Coralline Oolite. 



In its area are included the Common of Thrupp and the wooded 

 Common of Appleton, but there is little variety in the vegetation. 



Among the plants which are found on the Oxford Clay, but which 

 are by no means confined to it, are Pier is Echioides, Senecio erucifolius, 



I I have followed the spelling adopted by my friend the late Professor 

 A. H. Green. 



