55 



Kimmeridge Clay is interesting geologically for its varied 

 assemblage of animal remains that cover a wide range of types, 

 and economically from the occurrence of extensive seams of bitu- 

 minous oil-shales found interbedded within it. The growing 

 importance of mineral oils in modern life and industry has drawn 

 attention to the occurrence of oil-bearing deposits in Britain. The 

 extensive use of oil by the Imperial Navy makes it essential that 

 sooner or later our country should provide from its own mines a 

 fully adequate supply of that material. Mr. Winston Churchill, 

 when First Lord of the Admiralty, referred to the considerable 

 potential supplies of the Kimmeridge oil-shales. More recently 

 active investigations have been in progress on the Kimmeridge 

 Clay in Norfolk, where very rich seams have been proved. But 

 at present no oil is won on a commercial scale from any Kim- 

 meridgian deposits, though it is not too much to say that if they 

 had occurred in any other country than Britain, both capital and 

 industry would long ago have been adequately applied to them. 



In its development in the type locality, Kimmeridge Clay 

 forms the undercliff of St. Alban's Head on the east, and of Gad's 

 Cliff on the west. In both places the upper heights of the great 

 sea cliffs consist of Portlandian Sand and Limestone. The clay 

 forms also the basis of the Vale of Kimmeridge, which lies at the 

 foot of the scarp of the ridge of Portlandian rock and ends on 

 the coast as a fine section of high sombre cliffs, continuous for 

 five miles between Chapman's Pool and Brandy Bay. 



Kimmeridge Clay forms, with the Portland Sand and Lime- 

 stone, and the Purbeck beds of Marls and Limestones, the upper 

 division of the Jurassic Series. It rests upon the Corallian Lime- 

 stone with Oxford Clay, which, according to some classifications, 

 are also included in the upper Jurassic Series but more generally 

 in the middle. 



The extensive development of Kimmeridge Clay in the neigh- 

 bourhood of Kimmeridge is due to the operation of the upthrust 

 of the main Purbeck Anticline, which here attains its maximum ; 

 the axis running more or less west and east inland from the cliff 

 at Hobarrow Bay, where the lowest beds are elevated. The beds 

 dip sharply on the west under Gad's Cliff and at a moderate angle 

 towards the south-east beneath St. Alban's Head. It coiisists of 

 rather gloomy-hued shales with many partings of harder rock of 

 •clayey limestones, which, when weathered out by sea action, form 

 a series of ledges running for some considerable distances across 

 the foreshore. The many faults are emphasised by the distinct 

 partings of these hard belts. The bituminous shales occur in the 

 upper division of the clay as a few seams of " coal." 



The next exposure of Kimmeridge Clay along the Dorset 

 coast is at Ringstead, just past the high cliff at White Nothe. 

 In part it forms the basis of the cliff "below Holworth House, 

 where, together with Portlandian and Purbeckian beds, it is 

 •diagramatically overlapped by the Gault and shows that' it had 



