14 



a thin bed of shelly gravel abounding in many perfect specimens 

 and comminuted fragments of the same fossils ; to this succeeds 

 an equally thin bed of fine white loam, containing shells far 

 more perfect but less numerous." He had reason to think the 

 sand and the loam contained a somewhat different collection of 

 molluscs. He gives a list of 18 species. 



Prof. Sedgwick adds a note to Mr Brodie's paper, commenting 

 on the different kinds of Diluvial deposits near Cambridge ; 

 these he now groups into three divisions. 



(1) The great brown clay, forming the table-land between 

 Cambridge and Bedfordshire. 



(2) The coarse gravel, occupying the crests of the Gog- 

 Magog and Harston Hills, and containing fragments from most 

 of the older formations in England. 



(3) The fine flint-gravel of the plains, covered by the bog 

 earth and alluvium. 



He mentions bones of Mammoth and Rhinoceros as having 

 been found in the Brown clay(!), and cites the following mam- 

 mals as represented by bones from the Barnwell gravel : Mam- 

 moth (common), Equus (common), Rhinoceros (common), Bos 

 (very abundant), Hippopotamus teeth (rare), Cervus (several sp.), 

 Irish Elk (horns of). 



1845. At the British Association in 1845 Prof. Sedgwick 

 read a paper "On the Geology of the neighbourhood of Cam- 

 bridge\" wherein he gives some description of the Brown Clay, 

 noticing its contents, irregular thickness and distribution ; he 

 believes that 99 parts out of 100 of the whole mass are derived 

 from the country of the Great Fen Clay (lying to the north). 

 With regard to its origin he says that "Icebergs may during the 

 period (of submergence) have transported boulders to a great 

 distance and dropped them among the superficial deposits of 

 the country ; but no conceivable action of icebergs could have 

 scooped out the great hollow of the Fens and spread the 

 materials far and Avide over all the higher lands on the south- 

 east side of the Great Level." He further remarks that in the 

 neighbourhood of Cambridge there are no old local freshwater 

 deposits above the Brown Clay, like those found on the coast of 

 I^orfolk. The expectation implied in this remark is accounted 



* Tlep. Brit. Akxoc. Trans, of sections, p. 44. 



