642 STRATIGEAPHICAL GEOLOGY 



mentioned above, and it is only at these places that Rhinoceros 

 leptorhinus and R. tichorhinus have been found together. 21 The 

 presence of Rhinoceros megarhinus (a Pliocene form) and the absence 

 of the reindeer (Eangifer tarandus) are regarded as indications of the 

 antiquity of the deposits. Between fifty and sixty species of land 

 and freshwater shells have been found, several of which no longer 

 live in Britain, e.g. Cyrena (Corbicula) fluminalis, Unio littoralis, 

 Pisidium amnicum, Hydrobia marginata, and Helix fruticum. A 

 worked flake proving the presence of Man has also been found in 

 the lower brick-earth. Many flint implements of Palaeolithic types 

 have also been found in high-level gravels at Acton and Stoke 

 Newington on the north side of London. 



The district now drained by the river Cam contains an 

 interesting series of river deposits which bear testimony to the 

 successive changes that have taken place in the drainage system of 

 this area. 22 The oldest line of gravels has no connection with the 

 modern river -valley, but crosses it nearly at right angles near 

 Cambridge. Patches of gravel in the hill-valleys near Balsham 

 testify to the action of streams where none now exist, and these 

 seem to have united to form a river which ran by Wilbraham, Quy, 

 Cambridge, Girton, Oakington, Long Stanton, and Willingliam. 

 The deposits it has left now form long gravel-capped ridges, the 

 base of the gravels where intersected by the Cam being about 40, 

 and their surface sometimes 60 feet above the modern alluvium. 

 These fluviatile gravels appear to terminate abruptly near the fens 

 of the Bedford Level, but were probably originally continuous with 

 the gravels at Chatteris, Doddington, and March, which form 

 similar ridges rising above the general level of the fens which 

 surround them, and evidently mark the estuarine channel of a 

 river which traversed the country when it stood at a somewhat 

 lower level, and before the Fen-land existed. The shells found at 

 March are chiefly marine, but include Corbicula fluminalis. 



Of deposits which bear a definite relation to the modern river 

 Cam, remains of three terraces can be recognised. The highest of 

 them runs by Trumpington and Barnwell, about 25 feet above the 

 alluvium, and has yielded a number of mammalian bones and 

 teeth, with a still larger number of shells, among which Corbicula 

 fluminalis, Unio littoralis, and Hydrobia marginata occur. These 

 three shells do not occur in the lower terraces, which are respec- 

 tively about 15 and 8 feet above the alluvium near Cambridge. 



Lacustrine Deposits. Two notable instances of such deposits 

 occur in the east of England. That of Hoxne, near Diss in Suffolk, 

 is perhaps the best known, pits at that place exposing over 30 feet 

 of lacustrine beds without reaching the bottom ; the lower beds are 



