384 MICROTIN^ 



a reduced pair of salient angles (fourth outer and fifth inner) 

 forming the fore-part of the anterior loop; general form of the 

 tooth rather like that of M. newtoni or some forms of M. majori 

 in late stages of wear, the third outer fold rather deep and not 

 apparently reduced by insulation ; trfi with a persistent second 

 inner valley and in general form agreeing closely with those from 

 West Runton. 



Although the patterns of the few cheek-teeth which have been 

 obtained from the High Terrace Drift are such as characterize 

 adult rather than youngish stages of wear, little progress has been 

 made with the development of their roots. In the two mandibular 

 teeth (j%) the cement spaces are only just beginning to close 

 below; in the two maxillary teeth before me {m} and m^) 

 they remain entirely open. This circumstance and the character 

 of the m^ would appear to indicate that the High Terrace species 

 is most nearly related to M. majori and M. neivtoni, differing 

 from the latter in its larger size, and from both the species 

 mentioned by the more tardy development of the roots to its 

 molars. 



Remarks. — The few teeth upon which this species is based 

 were all obtained from a small pit, in the High Terrace gravel of 

 the Thames, which was opened many years ago at Ingress Vale, 

 near Greenhithe, Kent. These scanty remains are of great 

 importance, since they prove that the genus lingered on in southern 

 England until a comparatively late moment. Until recently 

 the majority of British geologists have accepted and maintained 

 the view that the High Terrace of the Thames is a " Post- 

 Glacial " deposit, in the sense that it was formed after the cul- 

 mination of the glacial period in south-eastern England. The 

 argument upon which this view is based was formulated before 

 anything of the palaeontology of the High Terrace was known, 

 and before a reasonable and coherent theory of the evolution 

 of the English river system had been developed. The High 

 Terrace fauna proves, however, in the clearest possible way 

 that there was no break in the continuity of the terrestrial 

 life of the region between Upper Pliocene and High Terrace 

 times. Numerous Pliocene relicts survived in south-eastern 

 England in the High Terrace period, that is to say to a date later 

 than that of their disappearance elsewhere. Among the mammals 

 so surviving may be mentioned, in addition to M. cantianus, 

 Trogontherium cuvieri, Bus sp. n., Hippopotamus, Elephas 

 antiquus, and Rhinoceros leptorhinus Cuv. (= R. megarhinus de 

 Christol) ; among the Mollusca Neritina grateloupiana, a Miocene 

 species. Nor is this all. A monkey, Macaca, has been determined 

 in the uppermost part of the Cromerian Upper Freshwater Bed 

 (a stratum known in consequence as the " Monkey Gravel "), 

 and this genus has been found, associated with Hippopotamus, 

 Elephas antiquus and Rhinoceros leptorhinus Cuv., in the early 

 Middle Terrace deposit at Grays Thurrock, Essex, i.e., in a deposit 



