Chiseldon to Coilingbourne. 



99 



and contains some very massive beds, as may be seen in some of the 

 road sections near Basset Down and Clyffe Pypard. 



The Mtddh Chalk. 



Abont three miles from Chiseldon Station the cutting enters the 

 middle or second division of the chalk ; the dividing line between 

 this and the lower chalk is marked by a line of hard nodnlar 

 yellowish chalk known as the Melboimie Rock, bnt sections where 

 this rock occurs are rare in this district. This nodnlar bed, however, 

 may be seen on the surface of the ground near the junction of the 

 lower and middle chalk. Unfortunately the cutting does not pass 

 through this Melbourne Rock, but it may be seen in a pit close to 

 the line. 



The middle chalk is whiter and purer than the lower chalk and 

 less argillaceous. Mints also begin to make their appearance, but 

 rather sparingly. 



This division of the chalk w T as laid down in a deeper sea than 

 the lower chalk, and at a considerable distance from land. 



It forms a distinct feature in the escarpment, as most of the sheep 

 down-land is on the middle chalk, which is thus of importance 

 agriculturally. 



The middle chalk in our district is thinner than the lower, being 

 only about 120ft. thick. Being thinner and the dip being the same 

 its outcrop is much narrower than that of the lower chalk, and thus 

 it covers a much less area on the north and west. This bed is 

 marked 4b in the diagram. 



The Chalk Rock. 



The divisional bed between the middle and the upper chalk is 

 known as the chalk rock. No good example of this bed is to be 

 seen in the cuttings, though a smooth hard cream- coloured bed 

 rather like part of it may be seen in the cutting south of the bridge 

 by Ogbourne Maizey. 



The chalk rock consists of five or six distinct beds of hard cream- 

 coloured limestone, each of which has a layer of hard green-coated 

 nodules at the top ; each layer forming a marked plane of separation : 



