r 4 6 MIDDLE ALBIAN STRATIGRAPHY 



From the foregoing brief description, the evidence for NW. to SE. trending ridges 

 and troughs is not conclusive, but is very strong. However, in the southern Weald 

 and the Isle of Wight three pieces of evidence, in the writer's opinion, tip the balance 

 strongly in favour of the interpretation here given. 



The spathi Subzone sequence expands southwards from Wrecclesham to reach 

 a known maximum thickness at Selborne. From there it thins southwards towards 

 Nyewood, but the lithological sequence in detail remains the same. Although there 

 is a partial facies change and the sediments are coarser in E. Hampshire and W. 

 Sussex, the sequence in the spathi Subzone at Selborne lithologically is remarkably 

 close to that of the Horton Clay Pit, Upper Beeding (text-fig. 14, opp. p. 42) where it is 

 underlain by a thick development of the lyelli Subzone. Yet this sequence at Horton 

 Hall is quite different to that seen at Storrington where the lyelli Subzone sediments 

 have not been proved and if present at all are very thin and pebbly. In the opposite 

 direction, at Hassocks, the eodentatus and lyelli Subzones sediments are still well 

 developed but are grittier and more glauconitic and here as at Storrington the Gault 

 rests upon an ' Iron-grit ' which forms the indurated top of the sands of the Folkestone 

 Beds. At Horton Hall, however, the tardefurcata Zone is represented within clays 

 and loams, totally different to that of Hassocks and Storrington. 



Along the WNW.-ESE. trending outcrop at the base of the South Downs from 

 Storrington to Petersfield, the Gault rests upon the ' Iron-grit ' (Kirkaldy 1935), below 

 which are normal loose sands of the Folkestone Beds. This sequence is seen at 

 Portsdown where the pre-Gault Lower Cretaceous sediments are greatly attenuated. 

 This area in which the ' Iron-grit ' is present at the base of the Gault marks a long 

 swell on the pre-Middle Albian sea-floor which apparently increased in amplitude 

 towards the ESE. (p. 34). The sequence on the other side of the trough at Hassocks 

 has already been mentioned, and from what little is known of the Lower Albian 

 sequence near Eastbourne, and the Middle Albian sequence at Ringmer, the trough 

 extended ESE. from Upper Beeding towards Eastbourne. The sedimentation 

 remains very thick along this axis and if one projects the line through Selborne 

 into Wiltshire it again coincides with a broader area of thick dentatus Zone 

 sedimentation. 



On the other, southern, side of the Storrington-Portsdown swell the lithological 

 sequence in the eodentatus, lyelli, and spathi Subzones in the Isle of Wight is totally 

 different from that of the Ringmer-Selborne trough. It is possible therefore, that 

 yet another WNW.-ESE. trending trough exists in the English Channel and which 

 includes the Isle of Wight. Both the mammillatum Zone sequence and the Lower 

 Gault increase in degree of representation towards the southern part of the Island. 

 The diachronous base of the Gault along the Dorset Coast can be explained if one 

 considers this line to be a diagonal section across the trough, the intermedins Sub- 

 zone sediments in the Charmouth area being near the southern bounding ridge which 

 may have flanked a positive area in view of the sequence in the Pays de Caux. 



In the E. and NE. part of the Weald the axes of the parallel ridges and troughs 

 trend as far as it is possible to judge in a NW. to SE. direction and they are with the 

 possible exception of the Kent Coalfield fairly closely set and linear (text-fig. 52). 

 The apparent opening-out of the troughs in the northern Weald W. of Dunton Green 



