﻿408 ME. E. M. BErDO^fE OX THE [Allg. I908, 



Cretaceous fauna of great abundance, nnd indistinguishable by any 

 physical or palaeontological character from the lower Grey Chalk 

 already dealt with or from an area of Grey Chalk to be dealt with 

 later. The boundary between this Grey Chalk in the Bluff and the 

 Ostrea-lunata Chalk beneath it, was marked in some places by a 

 seam of grit swelling out into a bed of grit with pebbles of flint 

 and chalkj but was marked in other places only by the sharp change 

 in colour and fossil-contents. The probability suggested in the 

 Geological Magazine (1906, p. 74, etc.) that the flints of this Grey 

 Chalk were in definite beds has been shown by further and better 

 exposures to be a fact, the large and perfectly silicified flints form- 

 ing a band at the base, and the smaller, carious, and imperfectly 

 silicified flints forming bands higher up. 



The next small area {t) requiring special notice is the Grey 

 Chalk already mentioned which occurs about 80 j'ards north-east of 

 the North Bluff. A cursory glance shows that it cannot be in 

 conformable sequence with the adjoining 0. Zmia^a-Chalk, and the 

 question arises as to whether the boundary-line is a fault or an un- 

 conformity. Such parts of the boundary-line as I have been able to 

 examine lend no support to the fault-theory, and afford but a feeble 

 presumption in favour of an unconformity. Fortunately the surface 

 of the Grey Chalk is deeply furrowed, and several of these furrows 

 have cut down to Ostrea-lunata Chalk, in one case with what 

 appeared to be a grit-seam at the boundary. I have, therefore, no 

 hesitation in saying that these beds are lying unconformably on the 

 O.-lunata Chalk, in which case they must be newer than any beds 

 exposed in the regular sequence in this block. These grey beds 

 correspond closely with the lower grey beds of this block, but even 

 more closely with the Grey Chalk on the jS^orth Bluff, seeing that 

 in both the characteristic fossils Ostrea canaliculata, 0. sulcata, and 

 Terehratula obesa are very abundant (especially 0. canaliculata), and 

 that they lie unconformably on different parts of the same set 

 of O.-lunata beds. They are, therefore, considered as probably 

 identical. 



A third special area (r) is that of Grey Chalk and Ostrea-lunata 

 Chalk to seaward of it which appears near the southern end of the 

 block. This area is low -lying and therefore very rarely cleared of 

 sand, but it appears possible that the Grey Chalk is identical with 

 the ' upper grey beds ' of opposite dip seen close by on the south. 

 Probably there is another fault dividing them from the O.-lunata 

 Chalk, but no certain identification of either the Grey Chalk or the 

 O.-lunata Chalk is possible. 



There are also two small exposures of hardened Grey Chalk (s) 

 at the southern extremity of the block, and these undoubtedly 

 formed part of the same bed. They are identical in fossil-contents 

 with the neighbouring ' upper grey beds ' ; but no stratigraphical 

 evidence concerning their relationship has been obtained, as they 

 appear to be isolated by clay. 



As some stress has been recently laid in argument on the relative 

 positions of the Chalk and the Boulder-Clay, it seems desirable to 



