1898] PROBABLE DEPTHS OF THE GAULT SEA 809 



Folkestone. The specimens from West well Leacon and Gods tone 

 are still clays, with no colouration, the tubular infillings being bluish 

 grey, whilst the Folkestone specimen is a clay ironstone. 



It is noteworthy of Zone III. at Folkestone, that owing to the 

 absence of pyritons infilling of the foraminiferal shells, they are 

 much paler in colour than is usual with Ganlt specimens of 

 foraminifera. 



The conditions in this zone seem to have been favourable for 

 the Crustacea, and by their abundance this bed is known to collectors 

 of fossils as the ' Crab bed.' At this horizon Ostracoda are especially 

 abundant. Globigerina cretacea also forms a fairly large proportion 

 of the washings. 



From the evidence of the foraminifera, the depth of this deposit 

 was 1180 fathoms. 



The character of the clay makes it appear to have been originally 

 a red mud of a semipelagic nature. 



Zone IV. — The clay of this zone is greenish grey. The foramini- 

 fera are very minute, owing to the prevalence of muddy matter, and 

 the scarcity of dissolved calcareous material. 



This clay is probably represented in modern deposits by blue 

 mud rather than green mud, since glauconite, although present, is 

 only in a small proportion in the washings. 



The depth determined for this zone is 840 fathoms. 



Zone V. — A grey-blue clay spotted with lighter markings. 

 The washings contained a large proportion of Globigerina cretacea, 

 Sphaeroidina bidloides also being found. 



This deposit seems originally to have been a blue mud, from 

 the quantity of pyrites found infilling the foraminiferal shells and 

 elsewhere, and from the small quantity of glauconite present. 



The depth determined by the foraminifera is 750 fathoms. 



Zone VI. — This is a mottled blue-grey clay. There is much 

 pyritous material as in Zone V. The deposit appears to be equiva- 

 lent to the blue muds. 



The probable depth is 790 fathoms. 



Zone VII. — A dark blue-green clay, which from the scarcity of 

 glauconite and the presence of pyrites, must have originally been a 

 blue mud. This and the next zone above seems to have been formed 

 under conditions particularly favourable for the existence of the 

 redundantly grown Pidrimdina spinulifera. 



The depth for this zone is 810 fathoms. 



Zone VIII. — A grey clay, with a little glauconite in the fine 

 washings. This also can be classed with the blue muds. The ferric 

 carbonate casts become scarcer from Zone III. upward, and are 

 entirely absent in this zone, so far as I have observed, but they 

 again recur in the next and succeeding zones. 



