CHAP. XI.] HANTONIAN PEEIOD. 219 



the Wealden area, producing the first outline of the oval 

 or boat- shaped periclinal of this area, it is easy to under- 

 stand the relations of the several members of the Lower 

 London Tertiaries ; at first the shores would be low and 

 cliff-less, but the general submergence at the time of the 

 Woolwich and Eeading Beds would convert the Wealden 

 dome into an island, and the erosion of the waves along its 

 margin would lead to the development of cliffs, at the foot 

 of which shingle beaches would naturally be formed. 



In this conclusion, and except as to the precise epoch 

 when the pebbles were first quarried from the chalk, I am, 

 indeed, only following Professor Prestwich's original view, 

 which is expressed as follows : l " From the foregoing con- 

 siderations it is probable that there was some extent of 

 dry land, possibly an island, somewhere intermediate 

 between a line drawn, on the north, from Farnham toward 

 Canterbury, and on the south from Winchester to New- 

 haven, and extending eastward into the north of France ; 

 and that the long- continued wear on its coast accumulated 

 on its shores extensive banks of pebbles, whilst the finer 

 sediment produced at the same time, in conjunction with 

 the debris brought down by operation of streams, formed 

 at a distance from the land the strata of this oldest Eocene 

 epoch." 



Let us next consider the evidence of the plastic clays of 

 the Reading group, and the physical conditions which 

 their characters appear to indicate. It is the general 

 opinion that they are of freshwater origin. Their asso- 

 ciation with plant beds, and their actual intercalation be- 

 tween freshwater deposits near Paris, are strong pieces of 

 evidence in favour of this view ; but if they are fresh- 

 water beds, it is difficult to see how they can have been 



1 " Quart. Journ. Geol. Soc.," vol. viii. p. 259. He then thought the 

 pebble beds were formed during the deposition of the Thanet Sands, 

 and were afterwards redistributed. 



