THE LONDON CLAY. 31 



The London Clay is an important member of the Tertiary or 

 newest of the three great divisions of the Sedimentary rocks. In 

 England the Tertiary rocks (clays and sands are " rocks " in 

 geology) occupy now two distinct areas, separated by a con- 

 siderable distance from each other. These areas are called 

 " Basins " from the beds having an inclination from both sides 

 of the area towards the interior, and thus we have the " London 

 Basin " and the " Hampshire Basin." The latter includes the 

 southern portion of Hampshire and the northern portion of the 

 Isle of Wight, and is separated by the Chalk area between Win- 

 chester and Basingstoke from the London Basin which extends 

 eastward from the foot of the Marlborough Downs, both south 

 and north of the 7'hames, to the sea, and, broadening eastwardly, 

 it forms a more or less triangular area between the Chalk of 

 Hampshire, Surrey, and Kent on the south, and the Chalk of 

 Bucks, Herts, and Suffolk on the north. 



The whole of the Tertiaries are divided into the Eocene, or 

 lowest and oldest, the Miocene, the Pliocene, and the Post- 

 Pliocene, the uppermost and newest, and the London Clay is a 

 member of the lower division of the Eocene group of strata. 

 The lowermost formation of the Eocene in England is called the 

 Thanet Sands, and reposes on the Chalk the uppermost of the 

 Secondaries. The Thanet Sands are followed by the Woolwich 

 and Reading Series, and in Kent by the Oldhaven Beds. Over- 

 lying these formations, which are collectively named the Lower 

 London Tertiaries, is the London Clay, a much more considerable 

 deposit than either of the others. This vast accumulation of 

 argillaceous matter extends, as before stated, from Hungerford in 

 Berkshire to the German Ocean, its most eastern point being at 

 Harwich, its greatest southern extension is near Canterbury, and 

 its most northern at Sudbury on the northern border of Essex. 



