286 NEOZOIC TIME. [CHAP. XIII. 



which the Pliocene period seems to have closed was not of 

 long duration, and that it was succeeded by a movement 

 of upward tendency. One proof of this is the occurrence 

 of a peculiar bed containing Arctic plants and animals 

 and small land-shells between theLeda myalisbed. and the 

 lowest Boulder-clay of the Norfolk coast. The fauna and 

 flora of this bed (so far as at present known) are so very 

 different from those of the Forest Bed below, 1 and so much 

 more Arctic in character, that the change in the climatal 

 conditions must have been very great, and could hardly 

 have taken place in a short space of time ; it would appear, 

 therefore, that the period of time which elapsed between 

 the formation of the Forest Bed and this Arctic plant 

 Bed was a long one, and that in the course of this unrepre- 

 sented time the whole of East Anglia, and probably the 

 whole of Britain, was raised far above the level of the sea. 

 This important conclusion, however, does not rest entirely 

 upon the evidence of the Arctic plant Bed, it is supported 

 by other facts, and especially by a consideration of the 

 tmried river- valleys which occur round our northern coasts 

 and the depth to which they were evidently excavated 

 during the interval between the formation of the Pliocene 

 and Pleistocene deposits of Norfolk. The position of the 

 latest Pliocene beds proves that the country at the close 

 of that period was at a rather lower level than it is now, 

 while the depth to which the valleys were cut before they 

 were filled with Boulder-clay proves that the land had at 

 some intervening time stood at a much higher level than 

 it does now. Thus the bottom of the valley formed by 

 the rivers which flowed through the gap in the Chalk 

 escarpment now filled by the Wash (see p. 256) is at 

 Boston 180 feet below the sea-level ; the pre-glacial channel 

 of the Tees is 200 feet below the sea, and that of an old 



1 See " Geology of Cromer," Mem. Geol. Survey, by C. Heid, p. 83. 



