Yol. 54.] CORALLIAISr EOCKS OF TJPWAEE. 611 



Considering the strong lithological and palgeontological resem- 

 blance between this Upware rock and the types at Elsworth and 

 St. Ives ; considering also the occurrence of a similar rock with 

 similar fossils at several localities in the neighbourhood of Elsworth 

 and St. Ives ; also between these places and Upware, at Bluntisham 

 on the authority of Prof. Seeley/ and at Chettering Farm, 2| miles 

 north-west of Upware, on that of Mr. Roberts, there can be no 

 doubt of the correctness of the correlation of this Upware rock 

 with that of Elsworth and St. Ives. At Upware, as at Elsworth, 

 according to Prof. Seeley, the series consists of three members, an 

 upper and a lower limestone separated by clay. The relative 

 thicknesses are, however, naturally somewhat different. The series 

 seems to vary somewhat, for at Chettering Farm there is said to 

 be 8 feet of Elsworth limestone under Ampthill Clay, and over- 

 lying 11 feet of light-brown sandstone. Little stress then can be 

 laid on any such identity of divisions at Upware and at Elsworth, 

 and an access of calcareous matter to the middle division at Upware 

 would " convert the whole into an uniform limestone of Elsworth 

 type. 



The upper limit of the Elsworth Rock at Upware must be more 

 or less arbitrary. It should, perhaps, be placed below the bed of 

 Thecosmilia, which forms the top of E in the well-section (p. 609), and 

 below 2 in the field-section (p. 606). The marl above, with its crys- 

 talline beds of Thecosmilia, and the Pe ntacrinus-'beds would then form 

 a passage. It is noticeable that Thecosmilia^ so abundant in the 

 lower part of these passage-beds, is quite unknown in the Rag and 

 oolite of Upware, but has been found at Elsworth. 



The lower limit bf the Elsworth Rock is easily fixed by the 

 well-marked band of Serpula, which Mr. Keeping states is per- 

 sistent at the top of the Oxford Clay throughout the whole district. 

 It is, he says, visible at the base of the Elsworth Rock at Elsworth, 

 and at the base of the Ampthill Clay at Gamlingay. At Upware it is 

 crowded with Serpula, intermixed with shells of Exogyra nana, etc., 

 and may mark a pause in deposition. Its matrix is clayej^, and above 

 it there seems to be 2 or 3 inches of clay with ferruginous oolitic 

 grains. A less definite Serpula-hauid occurs here in the clay between 

 the upper and lower Elsworth limestones. Mr. Thomas found it here 

 full of large crystals of pyrites. 



Mr. Keeping has carefully examined the ground for some distance 

 to the south and east. He has shown me that, although the 

 Upware Corallian type is represented by fragments on the surface 

 for a short distance south of the well, it is soon replaced by Els- 

 worth Rock and Elsworth fossils, which occur abundantl}'" both on 

 the surface and in the ditches for | mile south of the Inn. As 

 already mentioned (p. 610), he found Oxford Clay below it in a pit 

 which he had dug opposite the Engine Mill, at a point nearly as far 

 south as the last surface-indications of Elsworth Rock. One hundred 

 yards beyond this limit to the south he found the Upware Corallian 

 type again at the surface, till yet farther south it disappears beneath 



1 Ann. Mag. Nat. Hist. ser. 3, vol. x (1862) p. 101. 



