506 STRATIGRAPHICAL GEOLOGY 



The fossils in the lower zone are Rhynchonella Cuvieri, Inoceramus 

 mytiloides, Cardiaster pygmceus, Galerites subrotundus, Discoidea 

 Dixoni, and its variety minima. In the upper zone are Terebratu- 

 lina lata, Inoceramus Cuvieri, and Micraster corbovis ; here too 

 Spondylus spinosus makes its first appearance, and Holaster planus 

 comes in near the top. 



These beds can be traced all round the Wealden area, and 

 another fine exposure of them can be seen in the cliffs of Beachy 

 Head, where, however, there are no flints in the zone of Ter. lata. 

 In the Isle of Wight, Culver Cliff and quarries near Yarbridge 

 exhibit the following succession : 



Feet. 



fRough chalk with a seam of black clay in the 

 Zone of J middle and a layer of green-coated nodules near 

 Ter. lata j the base ........ 19 



V Thick-bedded white chalk with seams of marl . 90 



n c f Hard chalk, becoming nodular below and containing 

 T>, r . . \ many broken Inoceramus mytiloides ... 76 

 1 ( Rough nodular chalk with marly veins ... 8 



193 



Westward in Compton Bay the thickness is reduced to 150 

 feet. In Dorset, at Ballard Cliff, it is only 122 feet, but the same 

 layer of green-coated nodules occurs about 20 feet from the top 

 and has been mistaken for Chalk rock. At White Nothe Mr. 

 A. W. Rowe estimates its thickness at 134 feet. 20 



In Devon the Middle Chalk is well exposed near Beer, and is 

 about 100 feet thick, the zone of Rh. Cuvieri here including some 

 thickness of hard shelly chalk which is quarried for building 

 purposes, and is known as Beer stone. 



In the Midland counties this division exhibits the same litho- 

 logical and palaeontological characters as in the south of England. 

 In Berkshire it is not more than 150 feet, but north of the Thames 

 it rapidly thickens to about 220 feet, and maintains this thickness 

 into Suffolk. The Melbourn rock at the base is from 8 to 10 

 feet thick, and consists of hard nodular chalk ; it passes up into 

 bedded chalk, in which Inoceramus mytiloides and Rhynchonella 

 Cuvieri are generally abundant. The higher zone consists of soft 

 white chalk with layers of grey shaly marl and occasional nodules 

 of flint, which latter become more numerous towards the north, 

 till in Cambridge and Suffolk flints are frequent in this zone and 

 are often of elongate finger-like form. Fossils are seldom abundant, 

 but Galerites subrotundus and Terebratulina lata occur, with 

 Spondylus spinosus, Holaster planus, and Micraster corbovis in the 

 higher part. 



