316 THE RELATIONS OF THE CAMBRIDGE GATTLT AND GREENLAND. 



elusions. In the Cambridge deposit we have : — two distinct faunas — 

 one, as shown by percentages, related to the Chalk-marl, the other 

 to the Upper Gault ; two conditions of mineralization ; evidence of 

 erosion in the irregular junction of the two beds, in the waterworn 

 condition of many of the nodules, in the fact that they had Plica- 

 tulce, Polyzoa, &c. attached ; the nodules also could be detected in 

 the Gault, not only in the particular seam which had been described, 

 but at intervals throughout the mass ; also erratics of some size 

 occurred in the phosphate bed. These facts, he thought, proved the 

 existence of a break. He thought that associated bones were rarer 

 than Mr. Seeley described them to be. It appeared to him that some 

 of the speakers had forgotten that the question of the origin of the 

 nodules had already been brought before the Society by Mr. Sollas 

 and Mr. Fisher, who had shown very many of them to be phospha- 

 tized sponges. 



Mr. Whitaker said that the mapping of the parts of Bedford- 

 shire, Buckinghamshire, and Hertfordshire referred to in the paper, 

 for the Geological Survey, led him to conclude (in 1868) that the 

 nodule-bed is really the base of the Chalk-marl, there being a 

 regular passage upwards into the latter. He remarked on the 

 difficulty there often was of distinguishing between the lower part 

 of the Chalk-marl and the top part of the Gault before the nodule- 

 bed was laid open through the district he referred to. 



Mr. Hawkins Johnson said that the microscopical structure of 

 the phosphatic nodules is identical with that of septaria from the 

 London Clay, with that of the Clay-ironstone nodules of Yorkshire, 

 and with that of some septaria from the Kimmeridge Clay, and of 

 the phosphatic nodules from the Crag. Moderately thin sections 

 subjected to the action of dilute acid (even acetic acid), and examined 

 while moist, show a structure like that of sponge. 



Mr. Evans remarked that the difference between Mr. Jukes- 

 Browne and Mr. Seeley appeared to be on a question of fact. He 

 remarked upon the difficulty of distinguishing between the Chalk and 

 the Gault in Bedfordshire &c. 



Mr. Jukes-Browne, in reply, said that he was only concerned with 

 the question of where the coprolites had come from, and not that of 

 how they originated ; he had not therefore touched upon the formation 

 of phosphatic nodules. He thought Mr. Seeley had admitted some 

 of the most important points of his paper, viz. the eroded surface of 

 the Gault, the confluence of the Cambridge nodule-bed with that of 

 the Gault, and the consequent derivation of many of its fossils. He 

 must, however, maintain that there was a complete passage between 

 the Greensand and the Marl above, and no trace of a second line of 

 erosion, as Mr. Seeley appeared to think. "With regard to the 

 vertebrate remains, those preserved in dark phosphate were always 

 worn and rolled, while the associated bones Mr. Seeley spoke of were 

 light in colour, and undoubtedly belonged to the formation itself, 

 i. e. to the base of the Chalk-marl. Lastly, the lists and percen- 

 tages contained in the paper would show whether or not there was 

 a preponderance of Gault forms in the deposit ; and the author was 

 quite prepared to abide by observed facts and palaeontological results. 



