THE SOUTH-EASTERN COALFIELD 399 



Zone of Marsupites testudinarius. 



This zone, the highest in Kent, is formed of a pure, 

 dazzling white chalk, in which beds of flints are rare : it is 

 divided into prismatic blocks by numerous and well-defined 

 perpendicular joints, and it is this frequent parallel jointing 

 which gives the vertical face to the cliffs at Margate. 



A thin flint bed known as the " Bedwell line " divides it into 

 two sub-zones or bands : Marsupites testudinarius occurs com- 

 monly above, and Uintacrinus below it. The gigantic Ammonite, 

 Amm. leptophyllus, is well known in the cliffs between Birching- 

 ton and Kingsgate. The Uintacrinus-band differs from the 

 upper sub-zone in the replacement of the former crinoid by 

 the latter : a little belemnite, Aciinocamax verus, occurs 

 commonly in the lower band, replacing A. granulatus which 

 occurs in the upper. The Umtacrinus-band is 62 ft. thick in 

 Kent. 



It is only met with in one of the three collieries, namely at 

 Tilmanstone, where the top 30 ft. of chalk is in this zone. 



Zone of Micraster cor-anguinum. 



This zone is about 250 ft. thick on the coast of Kent. It 

 resembles the previous zone in its brilliant white colour, but 

 differs in the abundance of the beds of flint which occur with 

 remarkable regularity. The highly flinty chalk at the top of 

 the cliff under Dover Castle is in this zone, and the projecting 

 jagged fangs of the nodular flint beds are very striking. 



Beds of tabular flints sometimes occur : these are continuous 

 sheets of flints, and afford convenient measuring-points when 

 it can be shown that they are persistent ; but there is no doubt 

 that they sometimes pass into nodular flint, and vice versa. One 

 of the most important is the " 3-inch band " of Whittaker, which 

 can be traced from Kingsgate to St. Margaret's. It is a pro- 

 minent feature in the cliff, and is useful as a guide to the 

 junction with the overlying zone, which is exactly 21 ft. 

 above it. 



The fauna is relatively poor, especially near the base. 



Micraster cor-anguinum occurs throughout the zone, but also 



extends into the zone above ; a large urchin named Echinocorys 



scutatus, Breyn, is common enough, and has always a rounded 



utline : in the zone above, this urchin is distinctly pyramidal. 



