76 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 18, 



of basis for argument. The beds thinned out to the west and thick- 

 ened to the east. He was prepared to accept the two lobster-beds, 

 which in the section were one over the other, as merely showing the 

 persistence of the same bed, which, though continuous, had changed 

 its position during the interval. 



Prof. T. Rupert Jones considered that certain beds in the Wealden 

 were susceptible of correlation over very wide areas by means of 

 certain brecciated beds. He pointed out that near Pulborough and 

 at other places the Wealden terminated in paper shales, the same as 

 those which Mr. Meyer had placed at the top of the series at Pun- 

 field. Above these he thought no purely freshwater beds were to 

 be found. He considered that the whole, including the Wealden, 

 were included in the JNeocomian. 



Mr. Etheridge thought the difference between the various writers 

 on this subject to be mainly one of terms. The same fossils as those 

 found at Punfield had been found in abundance in Spain. 



Mr. Meter maintained, in opposition to Mr. Judd, that the Pun- 

 field beds were not merely Upper Wealden. He had found a certain 

 form of Ostrea over large areas always on the same horizon ; and 

 this had occurred at Punfield at precisely the level at which, in 

 accordance with his views, it ought to have been present. Above 

 the marine bands he had sought in vain for freshwater fossils. 



2. On the Coprolites of the Upper Greensand Formation, and on 

 Flints. By W. Johnson Sollas, Esq., Associate of the Royal 

 School of Mines, London ; Scholar of St. John's College, Cambridge. 



(Communicated by the Eev. T. G. Bonney, M.A., F.G.S.) 



[Abstract.] 



Part I. 



The first part of this paper was principally occupied in an endea- 

 vour to explain the perfect fossilization of sponges and other soft- 

 bodied animals. It was shown that the hypothesis which considered 

 that sponges had become silicified by an attraction of their spicules for 

 silica was altogether untenable. Mr. Hawkins Johnson's supposititious 

 reaction, according to which the carbon of animal matter is directly 

 replaced by silicon, was shown to be inconsistent with the known 

 facts of chemistry. The author's explanation was not intended to 

 be final. The first fact pointed out was the very remarkable way 

 in which the silica or calcic phosphate of the fossils under considera- 

 tion followed the former extension of organic matter. This was ex- 

 plained for silica by the fact that, when silicic acid is added to such 

 animal matters as albumen or gelatin, it forms with them a definite 

 chemical compound ; and it was assumed that in process of time this 

 highly complex organic substance would decompose, its organic con- 

 stituents would be evolved, and its silica would remain behind. In 

 such a way flints might be produced, and dialysis would lend its aid. 

 The same explanation was applied to account for the connexion 



