PROCEEDINGS OF THE COTTESWOLD CLUB 95 



200 feet. There is therefore a difference in thickness 

 between Leckhampton and Burford of about lOOO feet of 

 Lower Jurassic strata. Possibly it would be plainer if both 

 geological horizons are referred to the sea level. The base 

 of the Great Oolite at or immediately east of Leckhampton 

 would be 1000 feet above sea level, at Burford 20 miles 

 distant, and nearly due east, it is 400 feet above the sea ; 

 therefore the loss of Strata on the dip of the Great Oolite, 

 etc., from north-west to south-east is 600 feet in the 20 

 miles. 



Central or Middle (Cretaceous) Basin 



I have no intention of entering into particulars relative 

 to that portion of the Thames Basin termed the " Middle 

 Basin." 



The extensive area below Abingdon, Dorchester, and 

 the mouth of the Thame to Wallingford, and on to 

 Reading, Windsor, and Eton, are entirely upon the 

 Cretaceous Rocks, but it is important to notice the so- 

 called Middle or Cretaceous Basin as distinguished from 

 the Upper or Jurassic. The geological structure of the 

 Cretaceous area is much less complicated than the Jurassic, 

 which occupies or ranges from the highest part of the 

 western or north-western Watershed to Oxford and 

 Abingdon. 



The area occupied by the Cretaceous rocks may be 

 included in that part of the Thames Basin south of 

 Swindon, Abingdon, Thame, and Aylesbury; which line 

 determines their strike from the south-w^est to the north- 

 east. All to the south-east comprises the spread of the 

 Upper Greensand and Chalk, with an average breadth of 

 16 miles, to where it is overlaid by the Lower Tertiaries, 

 which trend or range parallel to the strike of the Creta- 

 ceous series above named. This extensive area occupies 

 1050 square miles. 



