84 ME. C. B. WEDD OliT THE CORALLIAN EOCKS [Feb. IQOI^ 



Discussioisr. 



Prof. Seeley spoke of the difficulty with which the Author had 

 met in mapping these thin and variable beds. The differences of 

 interpretation from that originally made by the speaker were in 

 matters of detail. He had been unable to trace continuity between 

 the Elsworth Eock and the St. Ives E-ock ; and there were other 

 stone-beds above the St. Ives Eock. By digging through the 

 Oxford Clay with Ammonites cordatus and Gryplima dilatata at 

 Elsworth, he had shown that the Elsworth Eock was in the Oxford 

 Clay. His fossils were placed in the Woodwardian Museum at 

 Cambridge. M. Eigaux found a similar rock with similar fossils 

 high up in the Oxford Clay of the North of Erance, though a little 

 lower than the Elsworth Eock. He was unable to accept the 

 present interpretation of the rock as Corallian, or as separating 

 the Ampthill Clay from the Oxford Clay, as an interpretation 

 warranted by the stratigraphical evidence. He found no stone 

 where Oxford Clay and Ampthill Clay meet. The fossils of the 

 Elsworth Eock, and still more of the St. Ives Eock, were interesting 

 from the circumstance that, in so far as some species diverge from 

 Oxford-Clay types, they resemble not only Corallian types, but 

 Cornbrash forms as well. 



Mr. H. B. WooDWAKD observed that the Author had done good 

 service in proving by careful 6-inch mapping the persistence of 

 the Elsworth Eock and its connection with the St. Ives Eock. He 

 suggested that the occurrence in the Elsworth Eock of the Lower 

 Corallian Ammonites perarmatus and the Upper Corallian A. plica- 

 tilis might be taken to indicate the local blending of the two zones. 



Mr. HuDLESTON observed that any attempt to relieve the monotony 

 of the Een clays by the discovery and identification of rock-masses 

 within them was worthy of commendation. The Author, chiefly 

 through lithological features, seemed to have recognized the well- 

 known Elsworth or St. Ives Eock at so many points that he had 

 been enabled to construct a ground-plan of the probable outcrop 

 throughout a considerable area. The palaeontological evidence 

 offered to the meeting had been scanty; but in the provisional 

 abstract there was some allusion to the fossils. They had already 

 heard from Prof. Seeley, who first brought the Elsworth Eock 

 under notice, that he regarded the fauna as uppermost Oxfordian. 

 Judging from the ample list of Elsworth-Eock fossils published 

 by the late Thomas Eoberts, it was impossible to avoid the con- 

 clusion that the rock at Elsworth occupies a very low position in 

 the Corallian Series. Indeed, whatever the Author's opinion on 

 this point might be, his ground-plan or sketch-map proved the case 

 pretty clearly. Here it is shown that the Elsworth Eock con- 

 stitutes the base of the Corallian Series in that area, since it is 

 represented as separating the Oxford Clay from the Ampthill Clay, 

 which latter clay is well-known to be the equivalent of the bulk of 

 the Corallian Series throughout the Eenlands. 



The Eev. J. E. Blake remarked that, although there appeared to 



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