IN THE ANGLO-PARIS BASIN 147 



is due partly to the fact that the outcrop tends to swing more parallel to the axes. 

 In the southern Weald the axes have swung WNW.-ESE. and the structures are 

 more open. These structures have what is normaUy considered to be an Armorican 

 trend, and the Middle Albian is the last time that such closely lineated structures are 

 fully identifiable in the depositional environment. 



(c) Source of the Middle Albian Sediments 



Middle Albian sediments ranging in age from the eodentatus Subzone to the 

 intermedins Subzone rest, outside the area of the Weald and the eastern part of 

 Hampshire, the Isle of Wight and part of Purbeck, and the area extending NE. of 

 Aylesbury, directly upon Jurassic rocks. These Jurassic rocks had been folded and 

 faulted in the late Jurassic-early Cretaceous to become land. Below the London area 

 andN. Kent the Lower Gault, when present, rests upon thin Lower Greensand which 

 is underlain by either Jurassic or Palaeozoic rocks. The Middle Albian sea, therefore, 

 was clearly transgressive far outstripping the depositional area of the Lower Green- 

 sand which itself oversteps the Wealden and both of which derived their sediments 

 from the Jurassic land area. It is evident from the cobbles and blocks included 

 in the mammillatum Zone sediments of Kent that Palaeozoic rocks of the London 

 Platform were by then undergoing active erosion. From the borings in N. and 

 E. Kent there is no evidence, however, that the London Platform contributed 

 any large quantity of sediment during the deposition of the Lower Gault. This 

 probably consisted only of the silty fraction which is mixed with a fine clay 

 fraction. 



In general as one moves west from the Kent coast the Middle Albian clays coarsen 

 in particle size and increase in the quantity of admixed silt and sand. This is readily 

 apparent if one compares for example in succession the sediments of the intermedius 

 Subzones at Folkestone, Buckland, in the Winchester borings, Devizes, and on the 

 Dorset coast in the Charmouth area. This suggests a main sediment source from 

 the western and north western margins of the sea, and possibly also from the south 

 in the area of the English Channel. 



On the coast in the Isle of Purbeck and towards Weymouth and in the Charmouth 

 area the diachronous base of the Gault can be seen to rest directly upon extensive areas 

 of Jurassic clays such as the Kimmeridge Clay, Oxford Clay, and the Lias (text-fig. 

 23). In the area of the Hampshire Basin, British Petroleum Co., borings at Bere 

 Regis near Wareham (Dorset) and at Fordingbridge (Hants) show the Gault to rest 

 directly upon Oxford Clay and Kimmeridge Clay respectively. Along the northern out- 

 crop the position is much the same (text-fig. 18), with Middle Albian sediments resting 

 upon the Lias in the far west and then eastwards upon an eroded surface of folded 

 Jurassic sediments in which the Oxford and Kimmeridge Clays bulk large. Now this 

 is the state of affairs within the area of the depositional basin itself already having 

 undergone erosion since early Cretaceous times. Moreover, this is the depositional 

 basin which extended rapidly during spathi Subzone times to its greatest known 

 Middle Albian extent in the intermedius Subzone. Without any question the 

 originally far greater depositional area of the Jurassic clays must have undergone 



K* 



