104 Mr. H. Seeley on Cambridge Geology : — 



necessarily infallible; the facts on which it is founded are too 

 few for it to claim to be more than an inductive guess. Indeed, 

 seeing that it is built fundamentally on the assumption that the 

 rocks at Elsworth and Boum are the same, it might be quite 

 wrong. All the facts certainly appear to be in its favour; but 

 it must not be forgotten that simplest explanations are often 

 truest; and in this case, if we suppose the country natter than 

 the preceding argument required it to be, the deep-seated rock 

 at Bourn (80 feet) would be continuous with the deep-seated 

 rock at Conington (100 feet) ; and therefore the rock at St. Ives 

 would be the Elsworth rock, and the band at Bluntisham pro- 

 bably identical with those in the bed of the Elsworth brook. 

 Nothing but its simplicity is known in support of this hypo- 

 thesis, which is only mentioned here as a contingency which has 

 not been overlooked. Even should it be ultimately proved true, 

 the result would in no way affect the principal object of this 

 paper, except in giving the arguments greater weight, by show- 

 ing that the Elsworth rock is really lower in the Oxford Clay 

 than it is now supposed to be. Meanwhile I adopt the explana- 

 tion previously given as the true one. 



It has already been seen that the St. Ives rock dips to the 

 east; therefore the Elsworth beds also will dip in the same di- 

 rection, and hence the clay to the east will be above the latter 

 deposit. 



Two miles eastward of Elsworth is Boxworth* ; and here the 

 land rises so that one can see over the Elsworth valley and the 

 country north and north-east of it. Now, on the easterly slope 

 of this hill is a brick-yard ; and here also is a rock, about a foot 

 and a half thick. The workmen call it " flint/' a name I have 

 also found given in the surrounding district to the septarious 

 concretions of the clays. It is dark blue, very hard, and divided 

 into layers, much as is the Elsworth rock. The only specimen 

 of it I saw was a slab from the upper part, about six inches in 

 thickness, which consisted of two layers— an upper dark-blue one, 

 with a few small shells scattered about in it, and a lower pale- 

 brown layer composed almost entirely of shells, chiefly univalves. 

 From the rock I only succeeded in obtaining, in a determinable 

 condition, Ammonites biplex, part of another Ammonite, appa- 

 rently alternans, Pecten lens, and a new species of Pecten, also 

 found at Elsworth, Alaria bispinosa, and Cerithium muricatum. 

 In the clay beneath I found a single specimen of Ostrea del- 

 toidea, another of Gryphaa dilatata, and two or three of an Oyster 

 nearly resembling O. laviuscida, hereafter to be described as O. 

 discoidea. This same Oyster occurs somewhat sparingly, with 



* Pronounced Els'cr and Box'er. Papworth is sounded Parper. 



