326 



The Geology of Devizes. 



I 



Fig. 4 Fig. 5. 



Figs. 4 and 5. — Structure of Melbourn Rock and of Chalk Rock 

 (magnified fifty times). 



but in it are scattered immense quantities of small round bodies 

 which are either the cells of Foraminifera or of some allied organisms. 

 Foraminifera are minute creatures which abound in all the seas and 

 oceans of the present day, some living in shallow water, and some 

 only in the open ocean. They extract carbonate of lime from the 

 water, and construct tiny shells perforated by small holes, and these 

 shells, either perfect or in fragments, have contributed largely to all 

 parts of the Middle and Upper Chalk. A common form (Globi- 

 gerina) is seen in the lower part of Fig. 6, and the small round 

 bodies occurring in the surrounding material are nowhere so 

 numerous and so robust as in this part of the Middle Chalk. The 

 quarry below the butts on Roundway Hill is opened in this Chalk, 

 and it forms the steepest part of the slopes round Oldbury Hill, 

 Morgan's Hill, and of the Downs that border the Vale of Pewsey. 



Chalk Rock. We now come to another well-marked horizon on 

 the Chalk, and one that was first described from a section in Wiltshire. 

 This is the Chalk Rock which has been worked for road metal in so 

 many places on the Chalk hills, both to the north and south of 

 Devizes. This rock is a hard white Limestone, lying in courses 



