Geological Society of London. 333 



derived from Litiiola, Rotalina, Glohigerina, and other forms. Some 

 green grains of exactly the same nature had been found by the 

 author in the siliceous sand of Blackdown. 



Discussion. — Prof. Phillips was glad that his casual remark had produced such 

 satisfactory results as the paper he had heard. It was satisfactory to find that the 

 bulk of the phosphatie nodules exhibited such marked traces of an organic origin. 

 Though he had to some extent been prepared for this, it appeared that the view might 

 be extended much further than would at first sight have been anticipated. He drew 

 an analogy between the preservation of the forms of sponges in their silicified fossils 

 with that of the soft organic bodies in the Greeusand by phosphatie matter. In such 

 case the surrounding water contained a large amount of either flint or phosphate of 

 lime, which was segregated and accumulated round certain centres or nuclei. 



Prof. Kamsay inquired from what sources the abundance of phosphatie matter 

 requisite for the production of these fossils could have been derived. In such thin 

 strata, which seemed to indicate a transition from a land to a marine surface, it was 

 a matter of great difl£culty to his mind to account for so great an abundance of 

 phosphatie matter. 



Mr. Godwin-Austen remarked that phosphorie acid was largely present throughout 

 all water, and instanced the present seas, where, as on the Newfoundland banks, fish 

 existed in enormous quantities, and no doubt also phosphatie matter. The Cambridge 

 beds, though so rich, were by no means unique of their kind. He referred to a paper 

 communicated some years ago to the Society by Mr. Payne, as aflTording many in- 

 teresting particulars with regard to such beds. He considered that much of the 

 phosphate attaching to decaying animal matter might have been derived from com- 

 minuted coprolitie deposits floating in the water. 



The Rev. T. G. Bonney remembered a fact quoted by the late Dr. Mantell as to 

 the large quantities of dead Mollusea which had been observed floating down some of 

 the American rivers, and which had been regarded as a plentiful source of phosphatie 

 matter. Small fishes might also have furnished a considerable quantity, and their 

 value as manure was recognized at the present day. With regard to the nodules 

 being Alcyonaria or sponges, he observed that what spicules he had seen appeared 

 more like those of sponges. He agreed with Mr. SoUas as to the Foraminiferal origia 

 ©f many of the green grains. He did not agree with Mr. Fisher in attributing all 

 the nodules to the bed in which they were found, but thought that a considerable 

 portion might be referred to the upper part of the Gault. In proof of the washing 

 the Gault near Cambridge had undergone, he mentioned the occurrence there of a 

 number of boulders of rocks quite foreign to the district. 



Mr. J. F. Walker thought that most of the fossils of the phosphatie 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 Greeusand 

 were absent, and the most abundant fossils were all of Gault species. It seemed that 

 wherever these accumulations of phosphatie 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. Whitaker observed that the Upper Greeusand thinned out as much, to the 

 south as to the north of London. He inquired as to the alleged abundance of phos- 

 phate of lime in the upper part of the Gault. He doubted whether the thin band at 

 Cambridge could represent the great thickness of Upper Greeusand 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. Meyer thought that the Greeusand had always been absent in the Cambridge 

 district, and mentioned the occuiTence of a bed of much the same character as that in 

 question at Niton in the Isle of Wiglit. 



Mr. Forbes pointed out that the amount of phosphatie matter in fishes was so small 

 that it was difficult to assign such an abundance as that described to this source. In 

 a mass of limestone composed of shells, he could find but 2 per cent, of phosphate of 

 lime. Even with true coprolites, he thought that they had become richer in phos- 

 phate since their first deposit ; but whence it was derived he would not pretend to 

 say. He thought this question of derivation still open. 



