310 NATURAL SCIENCE [November 



The evidence of the foraminifera points to 700 fathoms for the 

 depth of this deposit. 



Zone IX. — A dark blue-grey marl. Glohigerina cretacea is found 

 in some abundance, and from thence through the succeeding zones 

 increases in quantity until near the top of the Gault. The deposit, 

 compared with recent accumulations, might be termed a grey terri- 

 genous ooze. 



The foraminifera indicate a depth of 910 fathoms. 



Zone X. — A pale green-grey marl. This zone perhaps more 

 nearly foreshadows conditions which obtained in the Chalk-marl 

 than any of the others. The proportion of calcareous matter is very 

 large (as much as 45%) ; at 45 ft. from the top — in Zone XL it 

 was 36%; the Chalk-marl of Eastwear Bay at 10 ft. above the 

 ' Chloritic ' marl gave 67i% of calcareous matter. The conditions 

 existent then in Zone X. must have been favourable for calcareous 

 shelled organisms. Here particularly we obtain a great variety 

 of the strong shelled and costate forms of the genera Nodosaria, 

 Frondicularia, Margimdina, and Vaginulina ; and it was from this 

 zone more especially that the redundant and abnormal forms described 

 in my systematic papers (see Part X. Foraminifera of the Gault of 

 Folkestone) were obtained. This deposit may be classed with those 

 of modern date as a grey terrigenous ooze, and had a probable depth 

 of 900 fathoms. 



Zone XL — This bed, measured up to the base of the green-sand 

 seam, is a pale grey marl. Globigerina cretacea considerably increases 

 in abundance, and attains its maximum profusion at 45 ft. to 25 

 ft. below the top of the Gault, as well as in the next zone at 20 ft. 

 from the top. 



This bed can be compared with a grey terrigenous ooze, and 

 appears to have been deposited in 870 fathoms. 



Zone XII. — A glauconite-marl. A noteworthy point about this 

 deposit is that the glauconite casts have been formed at a less depth 

 than that at which the associated foraminifera lived ; for the foramini- 

 feral tests seen intermingled with the glauconite casts in the wash- 

 ings undoubtedly belong to a later period than the originals of the 

 casts themselves ; these remarks also apply to the microzoic fauna of 

 the green-sand seam of Zone I. 



This deposit is to some extent comparable with the glauconite 

 muds, and its depth is indicated as 820 fathoms. 



Zone XIII. — A pale grey marl, perhaps to be compared with the 

 grey terrigenous oozes of modern deposits. 



The foraminifera indicate a depth of 830 fathoms. 



It is here necessary to refer to a few points in explanation of 

 the evidence afforded by the foraminifera alone, as regards the depth 

 of sea in which these organisms lived. 



