PROCEEDINGS OF GEOLOGICAL SOCIETIES. 



553 



east, and appears to be found again at High Papworth, west of Els worth. As 

 the St. Ives rock dips to the east, so will the Elsworth rock also, and therefore 

 the clay to the cast and south will be superior to it, while that to the west is 

 inferior. Passing then west to St. Neots, another rock occurs, and this would 

 seem to be very low down in the series, and not far removed from the zone of 

 the Kelloway rock. The St. Neots rock consists of thin layers of limestone, 

 which are alternate with thin beds of clay. 



Among the fossils in the Oxford Clay, at St. Neots, are Ammonites Dimcauii, 



A. spinosus, A. athlethus, A. coronatus, &c. The commoner forms at St. Ives 

 are Ammonites Maria, A. cordatus, A. Bugenii, A. Goliaihas? &c, &c. Of the 

 Ammonites in the clay above the St. Ives rock, no good list is known, but 

 among them are A. altemans, and A. babeamis. Both at Elsworth and Blun- 

 tisham, above the rock, the Grypluea dilatata is found abundantly, and oc- 

 casionally with it O&trcea deltoidea ; but to the south the latter fossil is more 

 abundant, so that at Tetworth the specimens occur in equal profusion, and in 

 combination with Ammonites Achilles, Belemnites eccentricus, Lima pectiniformis, 

 Serpc.la tetrogona, &c, &c. At Tetworth there is a thin band of rock, as there 

 is also at Gamlmgay; at Box worth, nearly, if not in the same position, there 

 is a rook of the same thickness; and to the east, beyond this the clay seems 

 to graduate imperceptibly up to the Kimmeridge clay of Cottenham. 



There is thus a great thickness of strata between the Oxford and Kim- 

 meridge clays, in which the fossils of both those deposits are intermixed, and 

 which represents the Coral-rag. That such a clay did exist might have been 

 inferred from the presence of the Coral-rag at Upware, and its limited exten- 

 sion beyond. The Upware limestone was a coral-reef out in an old sea, and it 

 must have necessarily happened that beyond the narrow limits of the reef a 

 deposit of a different kind would have been forming on the sea-bottom, far more 

 widely spread than the limestone. This formation is named the Tetworth clay.* 



A difficult question then arose as to the limits of the clay, for if it were re- 

 placed by Coral-rag, it would result that the Elsworth rock would be immedi- 

 ately beneath the Coral-rag on the one hand, and above the Oxford clay on the 

 other, and so would appear to be rather a member of the former series than of 

 the latter. However, the presence of such forms as Belemnites tornatiiis, 



B. hast at us, Ammonites vertebralis, A. biplex, A. perarmatus, A. Henrici, A. 

 canalicidatus, A. goliathus, &c, were held as conclusive evidence that it ought 

 rather to be regarded as the uppermost zone of Oxford clay. The upper 

 boundary of the Tetworth clay cannot be given with any certainty. And from 

 the want of sections it has not been found possible to subdivide the strata 

 above, as has been done below. 



Such is the Pen-clay. The rocks of its lower part do not appear to occur in 

 the south of England, though there are divisions of the clay corresponding to 

 those so strongly marked by their occurrence here. The Tetworth clay has 

 long been known to have an extensive southern development ; a portion of it 

 appears to have been mapped by the Geological survey as Oxford clay, just as 

 in one district Mr. Lucas Barrett mapped it with the Kimmeridge clay. 



The author concluded by expressing his indebtedness, for much kind as- 

 sistance, to the Rev. S. Banks, of Cottenham, the Rev. H. Dobson, of Els- 

 worth, to Mr. J. Carter, of Cambridge, and to Mr. J. J. Evans, of St. Neots. 

 _ Malvern Naturalists' Eield Club. — The last meeting of this dis- 

 tinguished club of observers of nature in the fields of research, was held at 

 Upton-on-Severn. 



The chief feature in the operations of the day was the examination of the 



* At the Manchester meeting of the British Association, the name of Bluntisham clay wag 

 suggested for it, but as the section there is no longer visible, it has been thought better to 

 name it from a locality where it may be seen and worked. 



YOL. IY. o Q 



