BRITISH FOSSIL SPECIES 131 



Explanation of Fig. 66. 



I, 2, 3 and 4. M. nivalis Martins. Recent; Apennines, Italy (Dr. Forsyth 

 Major). 

 5. M. agrestoides Hinton. Right nii. Pleistocene; Grays. 

 6-14. 31. nivalis group. Pleistocene; Middle Terrace deposits, 

 Crajrford. 

 15. 31. nivalis group. Middle Terrace, Wicltham. 

 16-23. 31. nivalis group. Pleistocene; Clevedon Cave. 

 24-27. M. malei Hinton. Pleistocene; Clevedon Cave. 



28. Microtus sp. Clevedon Cave. 



29. 3Iicrotu8 sp. Middle Terrace, Crayford. 



water Bed of Bacton. These facts and those mentioned above in 

 connection with the High Terrace appear to show that the 

 Cromerian beds on the one hand, and the High and early Middle 

 Terrace deposits of the Thames on the other, are in part con- 

 temporary, and may in fact be regarded as parts of one great whole. 

 Confirmation of this view may be found at Piltdown, where in a 

 deposit that is evidently the stratigraphical equivalent of the 

 High Terrace of the Thames, the remains of a fauna still more 

 ancient than that represented at Ingress Vale have been found. 

 Eoanthropus, Mastodon, and Stegodon are genera which might well 

 carry us back to Norwich Crag times. These facts and deductions 

 have a not unimportant bearing upon the question as to the date 

 of the major glaciation of Britain ; but that is a subject which I 

 have discussed elsewhere.^ 



c. Late Middle Terrace of the Thames (typical locality, 

 Crayford and Erith). The following species are known : — 



"fDicrostonyx gulielmi Sanford. 



*Lemmus lemmus Linnseus. 



* Microtus nivalis group. 



ifMicrotus malei Hinton (and allied forms). 



*Microtus ratticeps Keyserling and Blasius. 



Between Early and Late Middle Terrace times the Microtinse, 

 together with most of the other mammals of Britain, were com- 

 pletely changed. Old forms, surviving in a more or less modified 

 condition from the Pliocene period, now became extinct, and were 

 replaced by an entirely new assemblage. Microtine remains occur 



^ Hinton and Kennard, " The Relative Ages of the Stone Implements 

 of the Lower Thames Valley," Proc. Geol. Assoc, 19, p. 76, 1905. 



Hinton and Kennakd, " Contributions to the Pleistocene Geology of 

 the Thames Valley. 1. The Grays Thurrock Area." Part II, Essex 

 Naturalist, 15, p. 56, 1907. 



Hinton, " Preliminary Account of the British Fossil Voles and Lem- 

 mings," Proc. Geol. Assoc, 21 p. 489, 1910. 



Hinton, " Rivers and Lakes," London, Sheldon Press, 1924, pp. 49-177. 



Hinton, " The Pleistocene Mammalia of the British Isles and their 

 bearing upon the date of the Glacial Period," British Association, 

 Southampton, 1925. (In the press. Yorkshire Geological Society's Pro- 



"" •) 



