-Vol. 52.] PHOSPHATIC CHALK AT LEWES. 473 



Discussion. 



Dr. W. F. Hume remarked that it is notable that the phosphatic 

 -chalks in England are not only so rare, but are also connected with 

 nodular conditions. The Middle Chalk in the South-East of England 

 has usually two prominent zones of nodular character — one at the 

 base, the Melbourn Rock ; the other at the summit, the Chalk Rock. 

 Between these the chalk is fine-grained, and only contains minute 

 fossils. At Lewes, however, the conditions are somewhat different, 

 the nodular conditions being several times repeated, while pebbles, 

 fragments of wood, large Inocerami and Ammonites, all suggest the 

 possibility of current-conditions at this particular locality. It is 

 therefore particularly interesting to find the phosphatic chalk here. 

 It is also noticeable that the foraminiferal fauna, as mentioned by 

 Mr. Chapman, has here a deeper aspect than that at Taplow, the 

 same statement holding good when compared with the Lower Chalk 

 foraminifera. 



Dr. G. J. Hinde could confirm the very close resemblance of the 

 Lewes phosphatic chalk to that of Taplow. He did not agree with 

 the Author in considering the deposit of shallow-water origin, for 

 microscopic sections showed that the rock was a purely organic 

 deposit without admixture of clastic materials ; it was, in fact, 

 similar in its constituents to a Globigerina-ooze, and was probably 

 formed under much the same conditions of depth as this latter. 



The Author was interested in hearing from Dr. Hume of an 

 abnormal character in the Chalk near Lewes; such observations 

 tended to throw light on the origin of phosphatic chalk. His inference 

 as to the shallow-water origin of the deposit was founded on ob- 

 servations made in the Challenger Reports on the formation of 

 glauconite and phosphate. He agreed with Dr. Hinde as to the 

 absence or great scarcity of clastic material. The term 'shallow 

 water ' required definition : by it he meant any depth between 200 

 and 600 fathoms. Undoubtedly the phosphatic chalk strongly 

 resembled Globigerina-ooze, in fact the plate in the Challenger 

 Reports illustrating phosphatized ooze would serve also for phos- 

 phatic chalk ; but in the latter glauconite has been formed in some 

 abundance, and we learn from the Challenger Reports that this 

 mineral is not now being formed in truly pelagic deposits, such as the 

 Globigerina-ooze. 



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