56 



been subject both to tectonic folding and denudation in pre-Cre- 

 taceous times. 



About Portesham, Kimmeridge Clay appears as fairly exten- 

 sive but strictly local exposure. It also forms the basis of the 

 Isle of Portland as an overgrown and obscured undercliff on the 

 north of the Isle. 



Kimmeridge Clay runs more or less continuously from Dorset 

 inland across England to the Wash as a member of the Jurassic 

 belt, forming much of the floor of the clay vale lying between the 

 chalk escarpment and the oolitic and liassic escarpments further 

 north. In North Dorset it thus forms much of the soil of the 

 Vale of Blackmoor, which in old times was heavily wooded with 

 oaks, but has now long been the pasturage of great herds of 

 cattle, and so well named by Thomas Hardy as the "Vale of 

 Little Dairies." In Wiltshire it is well developed as one of the 

 series of Jurassic rocks, for which th ; s country is famous, and 

 comprises much of the Vale of Wardour and most of the Vale 

 of the White Horse, and is here also famed widely for its dairy- 

 lands and locally for the bricks and tiles made from its material. 

 In Berkshire, as in Oxfordshire, it is maintained, though of little 

 thickness. It is almost entirely missing in Bedfordshire, though 

 it reappears just across the Cambridge border in strong develop* 

 ment. It forms the floor of much of the Fen district, and the 

 mass of the several " isles" which were practically the only dry 

 land in times past and on which most of the towns and villages 

 stand. The Clay of Norfolk has recently come into more promi- 

 nent notice, from the successful search for oil shales. In a len- 

 ticular depression, with its centre near the village of W T ormegay, 

 b : tuminous shales are interbedded with ordinary shales, and from 

 these oil has been obtained. Here the series appears to have 

 suffered a fair amount of denudation immediately after consolida- 

 tion, for the Portlandian and Purbeckian rocks are both missing. 

 Kimmeridge Clay forms the floor of the Vale of Pickering between 

 the North York Moors and the Wolds, but its only decent ex- 

 posure is on the coast in Speeton Bay. The ancient Kim- 

 meridgian sea extended far northwards to the uttermost parts of 

 Scotland, for the formation is represented in Cromartv and 

 Sutherland by a thick and variable series of estuarine sandstones 

 in the lower part, and marine grits, shales and limestones above. 

 Near the Ord of Caithness it consists of rough blocks of derived 

 rock mixed with the fossilised timbers of trees that had been 

 washed down into the sea from the Scottish Highlands of the 

 period. 



In addition to these evident exposures of Kimmeridge shales 

 are several concealed basins where they have been proved to occur 

 in considerable development. These are the concealed bas ! ns of' 

 the Weald of Sussex, of Kent, and of Saffron Walden. 



The likelihood of the occurrence of Kimmeridge Clav in 

 Sussex was very earlv recognised from the outcrop of Purbeckian 

 rocks near Battle. The famous sub-Wealden boring made in 1872' 



