INTRODUCTION xlv 



Then a wJiile later the river ceased to excavate, and ran at the lower 

 level it had reached long enough to develop a second alluvial flat. 

 When deepening was resumed, most of this was carried off, there 

 remaining only the patches that are seen in the terraces next below. 

 And so the process went on. 



The alluvium of these terraces is styled High-level Alluvium. 

 Examples are to be found close to Oxford, the city itself being 

 built upon a terrace which is some 20 feet above the present alluvial 

 flat and is covered by gravel from 8 to 16 feet thick. A correspond- 

 ing terrace is found on the Berkshire side of the stream at Wytham 

 and North Hinksey. In this deposit about Oxford abundance of 

 fossils derived from Jurassic rocks have been found. Bones of 

 the mammoth, rhinoceros, hippopotamus, ox, and deer occur in it, 

 while at Wolvercote, in a still higher terrace, worked flints have 

 been found. At Culham a broad expanse of this gravel rests on the 

 Gault, Greensand, and Kimeridge Clay, and remains of Elephas mitlqum 

 have been found in it. The Low-level Alluvium occurs very exten- 

 sively about Abingdon and Kadley, at Clifton Hampden, Wittenham, 

 Wallingford, Beading, Henley, and Aston ; a considerable breadth of 

 gravel occupies the valley at Culham Court, near Hurley, and reaches 

 to the cliff-foot at Bisham, while from Cookham to Maidenhead it 

 is widespread and of a most interesting character. It occurs also 

 between Maidenhead and Windsor, and on the east side of the 

 Loddon for two or more miles south of Twyford. About Kuscombe 

 it forms a higher terrace, and is seen along the course of the Kennet, 

 having a thickness of 24 feet at Newbury and extending as far as the 

 eastern foot of Enborne Hill. The level country to the north-east of 

 Burghfield is also covered with it. In the Hurley gravel many 

 remains of mammalia have been found. Here it is largely composed 

 of flints with chalk fragments, and, just as the fragments of the 

 Oolitic rocks found in the Hinksey gravel give a soil suitable for 

 Bromus ei-edus, so these fragments of chalk in the Hurley gravel are 

 the inducing cause for the continued presence of Campanula glomerata 

 and Scahiosa Columbaria, which grow in the meadows to which the river 

 floods have carried the seeds. At Newbury, where the gravel also 

 contains Chalk, the occurrence of AnthyllisVulneraria, ofPlcrisHieradoides, 

 and of Inula Conyza, is owing to the presence of the calcareous rock. 

 On the gravels near Maidenhead similar plants are found. 



Among the more interesting species found on the High-level Gravels 

 may be mentioned Potentilla argentea, Lactuca virosa, TrifoUum arvense, 

 Viola canina, TrifoUum striatum, Ornithopus perpusiUus, Eosa systy'a, Erigeron 

 acre, Filago apiculaia, F. minima, Calamintha arvensis, C. officinalis. Salvia 

 Verhenaca, Linaria repens, L. viscida, L. Elatina, L. spuria, Myosurus, Orohafiche 

 major [elatior), Verbena, Astragalus glycyphyllus, Arabis perfoliata, Arenaria 



