﻿406 METT^TTIT^BErDO^rE ON THE LAUg. 1 906, 



by any faults. In the centre of the anticline there is a considerable 

 thickness of White Chalk (Jc) with 0. lunata. This chalk covers a 

 large area in the northern part of the block and reappears at the 

 southern end in a small oval inlier. This is evidently a continuation 

 of the main ridge; but, as some O.-hmata Chalk also occurs a little 

 beachwards in more broken chalk where its extent cannot be 

 mapped, it looks as if the anticline were flattening out and splitting 

 up in this direction. Outside this 0. -lunata Chalk comes Chalk (Z), 

 only distinguishable from it by the total absence of 0. lunata^ and 

 outside that again more "White Chalk («i) with 0. lunata. I have 

 not noticed anything else that is especially remarkable about the 

 fossil-contents of these beds. Outside them comes finally Grey 

 Chalk (?i), which appears to be the highest of this sequence exposed. 

 This Grey Chalk is readily distinguished from the other Grey Chalk 

 of the block by the abundance in it of small Ostrea vesicularis and 

 the absence from it of Ostrea canaliculaia, 0. sulcata ( = incequicosiata, 

 S. Woodward), and Terebratula ohesa. It contains all the special 

 Trimiugham forms, except Ostrea lunata and probably Crania 

 spinulosa and Tliecidium vermiculare ; and in it were found my 

 only two specimens of Trigonosemus pulchellus and four of my five 

 specimens of Trigonosemus elegans. 



Only a small thickness of the Ostrea-lunata Chalk {Ic) in the 

 centre of the anticline would apparently have been exposed if the 

 beds bad remained unbroken, but a fault (o) has thrown up to 

 foreshore level the whole thickness of this Chalk and a considerable 

 thickness of Grey Chalk (p) underlying it. The westerly extension 

 of this Grey Chalk and of the lower beds of the central O.-lunata 

 Chalk is covered by permanent sand ; but, as they correspond in 

 the minutest details with the mass of Grey Chalk overlain by Chalk 

 with 0. lunata, which is seen on the same line of strike immediately 

 to the east of the North Eluff, they have been considered identical. 

 This Grey Chalk (p) contains (though not in abundance) Ostrea 

 canaliculata, 0. sulcata, and Terehratula ohesa (none of which have 

 yet been found in any but Grey Chalk at Trimiugham, and must 

 be exceedingly rare in the White Chalk there if they occur at all). 

 It also probably contains all the special Trimingham forms, except 

 0. lunata, Tliecidium vermicidare, and Trigonosemus pulcTiellus, 

 One specimen of Trigonosemus elegans has been found in it. Its 

 included flints are often of the smoke-coloured, soft, and poorly 

 silicified type described from the Grey Chalk on the North Bluff 

 in the Geological Magazine (1906, p. 74). These beds (Jc, I, m, n, 

 and p) alone play any real part in forming the block, and their 

 thicknesses may be estimated as follows : — 



Feet 



jO = Lower Grey beds 12 



k = Lower Osirea-lunata beds 20 



I = White Chalk without 0. lunata 8 



on = Upper O.-hmata beds 10 



w = Upper Grey beds (at least) 25 



7o 



