Correspondence — E. B. Tawney. 139 



Browne was fully justified in his conclusions. In the Cambridge deposit we have 

 two distinct faunas ; one, as shown by per-centages, 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 Plicatulce, Polyzoa, etc. 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 have shown very many of 

 them to be phosphatized sponges. 



Mr. Whitaker, from his experience in mapping the Geology of the Cambridge 

 district, came to the conclusion that the bed is really the base of the Chalk Marl, 

 there being a regular passage up into the latter. He questioned whether the 

 Upper Greensand is a separate formation. 



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. Moderately thin sections subjected to the action of dilute 

 acid (even acetic acid), and examined while moist, show a structure like 

 that of sponge. 



The President remarked that the difference between Mr. Jukes-Browne and 

 Mr. Seeley appeared to be on a question of fact. He -remarked upon the dif- 

 ficulty of distinguishing between the Chalk and the Upper Greensand. 



The Author, 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 phos- 

 phate 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 per-centages 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. 



C OIRZRIE S IPO ZEsTZDIE ICnTC IE . 



GIST THE CRETACEOUS AWRRKAIBM. 

 Sir, — In the February Number, your contributor, Mr. J. Starkie 

 Gardner, writing on Aporrha'is retusa, Sow., says, " I cannot find the 

 type or any specimen from Blackdown, and there is a doubt whether 

 the same species is intended." It is curious that he should appar- 

 ently not have read page 239 of Fitton's memoir, where it is stated 

 that his types belonged to the Bristol Institution, and are " now 

 in the Museum of that establishment." (See also Proc. Bristol 

 Naturalists' Soc, vii. pt. 2, p. 41.) In the Catalogue of Blackdown 

 Fossils, pp. 239-242, Fitton is very careful to indicate against each 

 species the collection in which the specimens may be found. Your 

 contributor also writes, ■' Should the Blackdown form prove distinct, 

 Deshayes's name of bicarinata must be adopted for it." We should 



