LONDON CLAY. 



99 



Section of the London Clay in Alum Bay. 



Fket. 

 Dark blue loamy clay, with ironstone nodules. Becomes 



sandy in the upper part - - - - - 46 



Laminated dark grey loam ----- 13 

 Loam, passing upward into fine sand - - - - 23 



Blue clay, becoming more loamy above - - -17 



Line of large septaria full of Cardita Brongniatii (a conspicuous 



bed) 

 Dark blue clay - - - - - - 62 



Loam with scattered small flint pebbles. Panopeea intermedia, 



Tellina, Gassidaria, Fusus, Turritella imbrieataria, Natica 



labellata ....... 2 



Brown and bluish clay, with lines of septaria - - - 35 



Septaria full of Pinna affinis (a conspicuous bed) 

 Brown and bluish clay, sandy in places, with lines of septaria 20 

 Basement Bed — Sandy glauconitic loam with a little pyrites. 



Ditrupa at the base - - - - - 15 



Total - - - 233 



Other measurements made the total 200 feet and 220 feet. 



Here again it must be observed that no reliance can be placed on 

 the minute accuracy of the measurements, for the top of the cliff will 

 give a different result from its base. If the monoclinal curve of 

 the Isle of Wight be carefully plotted and measured, it will be seen 

 that the upper and under surface of any bed affected by the 

 disturbance cannot always be paruilel, but that the thickness will 

 vary according to the part of the curve at which it is taken, and 

 also according to the hardness or softness of the beds affected. 



At Whitecliff Bay the basement pebble-bed, two inches in thick- 

 ness, is overlain by eighteen inches of buff-coloured sands, above 

 which there lies a bed of hard sandstone, abounding in JDitrupa 

 plana, that appears on the shore and may be seen stretching 

 out to sea, for a considerable distance, at low water. About 

 thirty-five feet above the basement bed there occurs a zone of 



Panopeea intermedia (Fiir. 19), and 

 Pholadomya margaritacea (Fig. 18), 

 with their valves closed ; at fifty feet 

 another band of Ditrupa plana (Fig. 

 20) comes in, and at about eighty feet 

 there is a well-marked band of Cardita. 

 The remainder of the section in 

 "Whitecliff Bay consists, in ascending 

 order, of lignite in dark-grey clayey 

 sand, aluminous and weathering to 

 a brown colour; ferruginous-brown 

 sands ; clayey sand or sandy clay 

 as before, but darker, harder, and 

 more clayey than the beds below, 

 and containing Panopwa intermedia, 



Fig. 18. 



Pholadomya margaritacea, 

 Sow. 



