56 Vertebrate Palaeontology of Cambridgeshire 



for the cetacean represented by this fossil, but in the following 

 year he changed 1 the title to Palaeocetus sedgwicki. It was 

 suggested by its describer that the specimen was derived from 

 the Kimeridge or Oxford Clay. This, however, is an altogether 

 untenable hypothesis, seeing that whales are unknown below 

 strata of Lower Eocene age, and that the forms from these 

 deposits are of an extremely primitive type, whereas the Ely 

 drift specimen conforms in all respects to the corresponding 

 portion of the skeleton of modern whales. A more probable 

 suggestion 2 is that the specimen was derived from the Red 

 Crag of the east coast, and that it belonged to one of the 

 species of beaked whales (Mesoplodon) so common in that 

 formation. Although it has been somewhat stained during 

 its entombment in the Boulder-clay, the specimen shows 

 distinct traces of having originally been of the reddish colour 

 characteristic of Crag fossils. 



Leaving the superficial deposits, we pass on to those of the 

 Secondary period, of which there is a succession, with some 

 gaps, in the county, from the Oxford Clay to the Upper Chalk. 

 The best chalk-pits in the county are those at Burwell, Cherry- 

 hinton, and Trumpington. Vertebrate fossils do not, how- 

 ever, appear to be very common in these pits ; at all events, 

 the published lists of species from the Chalk of the county are 

 meagre. The Lower Chalk at Isleham and the Chalk Marl at 

 Trumpington have yielded some fine jaws and numerous 

 teeth of the great marine reptile Ichthyosaurus campylodon, 

 which was one of the last survivors of the group so abund- 

 antly represented in the Lias. This species was established 

 by Mr J. Carter 3 , on the evidence of Cambridge specimens. 

 Certain small reptilian vertebrae from Cherryhinton, pre- 

 served in the Sedgwick Museum, have been made the 

 type of a distinct genus and species by Professor Seeley 4 , 



1 Geol. Mag. n. 54, pi. in. 



2 See Lydekker, Cat. Foss. Mamm. Brit. Mus. v. 31. 

 8 Rep. Brit. Assoc. 1845, 60 (1846). 



* "Index to Ornithosauria, etc." 3 (1869). 



