THE GEOLOGY OF THE LEA VALLEY. 20I 



with the Stort, as outhers of considerable size may be seen as far 

 south as Chigwell on the east and Finchley on the west. It can 

 scarcely be doubted, therefore, that the valley of the Lea with the 

 series of river-deposits which it contains are post-Glacial in age, in 

 the sense that they are of later date than the Boulder Clay of Essex 

 and Middlesex. Perhaps I may be allowed to add that in The 

 Essex Naturalist (vol. vii., pp. i — 13) I have given some account of 

 the evidence pointing to a similar conclusion in the case of the 

 Thames. Of course it is quite possible that there may have been 

 more or less low ground coinciding perhaps, here and there, with 

 that of the present valleys of the Thames and Lea, in pre-Cllacial 

 times. But the evidence decidedly favours the view that the valleys 

 as we now see them, with the series of river deposits at various 

 levels which they contain, are post-Glacial in the only sense in which 

 that term can be locally applied. 



Just below Tottenham High Cross the gravel flats of the Lea 

 become continuous with those of the Thames"; it therefore becomes 

 impossible to say whether the gravel about Walthamstow should be 

 considered to belong to the Thames rather than to the Lea, or the 

 reverse. From this point as far as the outfall of the Lea into the 

 Thames we may note, west of the marshes of the Lea, the broad 

 expanse of old river gravel on which London stands. And a 

 glance at the map of the Geological Survey will show us that 

 geological conditions which, as we have seen, led to the settlement 

 of a large village population on the western flank of the valley of the 

 Lea, equally decided the position of the great city of the Thames. 

 London has now far outgrown the limits of the site which must have 

 attracted inhabitants from the very earliest times. But if we confine 

 our attention to ancient London, now known as the " City," we learn 

 from the geological map that, as we ascend the Thames, this is the 

 first spot we come to which consists of a broad spread of river-gravel 

 of good elevation and yet close to the river ; at once capable of 

 being made into a place of strength and of yielding a good supply 

 of water. And we must not forget that ancient London, besides 

 the advantages already mentioned, had another in the existence of 

 the river Lea on its eastern side. For its presence furnished the 

 Londoners both with a valuable defensive outwork and with an 

 additional watery highway. 



