Vol. 54.] COKALLIAN ROCKS OF UPWARE. 615 



essentially Lower Corallian, and another of these, Millericrinus echi- 

 natus, is now recorded higher both in Yorkshire and in the South of 

 England ; other Elsworth species not found above the Lower Oolite 

 in Yorkshire are Goniocheirus cristatus, Ammonites convolutus^ 

 Nautilus perinflatus, Natica tenuis^ Avicula braambm-iensis, and 

 Waldheimia Hudlestoni, while Natica Ohjmenia, Avicula pteroper- 

 noides, Cypricardia glabra, Lima subantiquata, Waldheimia mar- 

 garita (?), and Cidaris florigemma are peculiar to higher Corallian 

 beds in Yorkshire. 



I have not been able to compare the Elsworth E-ock fauna with 

 that of the other English Corallian areas in the same way, owing 

 to the inclusion of Elsworth forms in the fauna of the perarmatus- 

 zone of the South of England, in the tables published by the Geological 

 Survey, some species being apparently so included only on the strength 

 of their occurrence at Elsworth and St. Ives. Perhaps Cidaris 

 Jlorigemma is an instance of this. There are some 71 species common 

 to the Elsworth and St. Ives Rock with the plicatilis-zone in the 

 South of England and at Upware. As regards the Oxford Clay 

 forms which occur in the Elsworth E/Ock, two more may be added 

 to them from that rock at Upware (Ammonites Eugenii and Rhyn- 

 cTionella varians) ; yet the base of the Elsworth Rock is here only 

 about 20 feet below a rock full of typical ' Rag ' forms. 



It is not, of course, suggested that the above comparison affords 

 any ground for placing the Elsworth Rock higher than the Lower 

 Calcareous Grit of Yorkshire ; but the foregoing statistics do seem to 

 show that there is no longer any palaeontological evidence for 

 correlating it with the Lower Calcareous Grit rather than with 

 higher beds. It is perhaps only another instance of the difficulty of 

 correlating distant Corallian rocks by fossil evidence, where faunistic 

 changes are due more to diflPerence of conditions than of horizon, and 

 most of the species have a wide range. It should be remembered 

 that the Elsworth Rock was first placed in the Oxford Clay, and that 

 anyone thinking it necessary to raise it to a higher horizon would 

 naturally correlate it with the Lower Corallian, in the absence of 

 decisive evidence for a still higher position. 



Of stratigraphical evidence for a correlation strictly with the Lower 

 Calcareous Grit there is of course none, if by ' Lower Calcareous 

 Grit ' we mean anything more definite than a local base of the 

 Corallian at whatever horizon. 



The precise relation of the Elsworth Rock at Upware to the 

 Corallian Oolite, whether the former constitutes the base of the latter 

 or passes into it- laterally, cannot be defcermined at present. The two 

 are certainly very closely associated. It is seen that there is 

 no intervening Ampthill Clay, unless the marly passage-beds above 

 and the clay between the two limestones of the Elsworth Rock are 

 to be regarded as such. Believing that the upper white limestone 

 of the field-section represents the true ' Rag ' horizon, I am rather 

 inclined to the opinion that the Elsworth Rock passes laterally 

 into the Oolite eastward and northward. StiU there is no real 



