1872.] SOLLAS — CAMBEIDGE UPPEE GEEENSAND. 401 



Mr. J. F. Walkee thought that most of the fossils of the phos- 

 phatic band at the base of the Chalk-marl were derived from the 

 Gault, whilst the bed differed from Chalk only by green grains 

 becoming gradually more abundant. The fossils were generally 

 much waterworn; the characteristic fossils of the Warminster 

 Greensand were absent ; and the most abundant fossils were all of 

 Gault species. It seemed that wherever these accumrdations of 

 phosphatic matter occurred, denudation had taken place, and that 

 they were the residuary heavy materials of a large thickness of rock. 

 This might also be observed in the Upware and Potton beds, 



Mr. Whitakee observed that the Upper Greensand thinned out as 

 much to the south as to the north of London. He inquired as to 

 the alleged abundance of phosphate of lime in the upper part of the 

 Gault. He doubted whether the thin band at Cambridge could 

 represent the great thickness of Upper Greensand which was to be 

 found in some other districts. He regarded it rather as a gradual 

 passage into chalk, though the line of demarcation was evident on 

 the Gault. Though agreeing with Mr. Walker as to some of the 

 fossils having been derived from the Gault, he could not regard them 

 all as having come from that source. 



Mr. Meyee thought that the Greensand had always been absent 

 in the Cambridge district, and mentioned the occurrence of a bed of 

 much the same character as that in question at Niton in the Isle 

 of Wight. 



Mr. Foebes pointed out that the amount of phosphatic matter in 

 fishes was so small that it was difficult to assign such an abundance 

 as that described to this source. In limestones all but entirely 

 comj)osed of shells, he could find only from ^ to 1 per cent, of 

 phosphate of lime. Even with true coprolites, he thought that 

 they had become richer in phosphate since their deposition; but 

 whence this phosphate was derived he would not pretend to say. 

 He thought this question of derivation still open. 



Prof. MoEETS mentioned the occurrence of similar deposits near 

 Wissant, on the coast of France, and near Calne, in Wiltshire. He 

 called attention to the extremely quiet nature of the sea in which 

 the phosphatic bed had been deposited, and observed on the existence 

 in recent times on certain sea-shores of ooze containing a large 

 amount of phosphatic matter. 



Mr. FisHEE, in reply, stated that he had in his paper but slightly 

 touched on the sources of derivation of the phosphate of lime ; but 

 as to the possibihty of that substance being localized and derived in 

 large quantity from fish, he pointed out that the principal manure 

 of modern times, guano, was derived from this source. He alluded 

 to the possibility of some process of dialysis having contributed to 

 the segregation of the phosphate. He disputed the identity of the 

 nodules in the Gault and in the chloritic marl of Cambridge. As 

 to the character of the fossils, he regarded it as the same as that to 

 be found in a thin band at the base of the Chalk in parts of 

 Hants and Dorset. 



