28 



TYPE AMMONITES— VI 



Aug. 



These may be compared with those in Oxfordshire 



C. Wheatley D. Shotover Brickyard 



It will be noticed that there are two gaps in these sequences, and that 

 really they cause all the trouble — one is the absence of Sands (No. 4) 

 from Aylesbury area, and the other is the absence of Hartwell Clay (3, 2) 

 from the sections of Wheatley and Shotover. But such non-sequences 

 are a well-known phenomenon in geology, for which the investigator 

 should always be prepared. 



These sequences may now be combined and dated as follows. For 

 further details see T.A. IV, 26-33 and T.A. V, 71. 



Numbers 



Table VI — Chronology 

 Hemerm 



Ages 



Dr. Neaverson (op. cit., 1924, 145) accepts the identity of Crendon 

 Clay with Lower Hartwell Clay, but places the Crendon Clay (2) as 

 equivalent to the Littleworth Lydite Clay (5), and then supposes that 

 the Littleworth Sands are the equivalent of the Thame Sands, which 

 makes the Thame Sands not of the same date as the Shotover Sands. 

 But this reading is disproved by the sequence shown in about the middle 

 of the Shotover Brickyard (D), where the Littleworth Sands are seen 

 overlying the Glauconitic Beds. Now the Glauconitic Beds, with 

 characteristic Ammonoids, are a most persistent and easily-recognized 

 stratum throughout the whole length of the Portlandian Lower Stone- 

 Beds (Behemothan) of Oxfordshire and Buckinghamshire. The 

 Glauconitic Beds overlie the Lydite Bed, which caps the Thame Sands. 

 The Hartwell (Crendon) Clay of the disused brickyard of Long Crendon, 

 which has yielded H. pallasioides and E. inflatum, underlies the Thame 



