PrimcBval Man in the Valley of the Lea. 105 
examination. The pebble-gravels also, such as one sees in 
the large pit in Silver Street, Edmonton, and on the higher- 
positions to the west of Enfield, are unproductive; these 
gi-avels are extremely ancient, and probably of marine origin. 
Lastly, the lower gravels in the immediate neighbourhood of 
and under the present streams are generally unproductive of 
implements ; they, however, now and then contain a stray 
example or two, undoubtedly washed down from a higher 
level. 
The productive gravels in the Lea Valley are almost in¬ 
variably those found between the 50 feet and the 100 feet 
contour-lines as marked on the Ordnance Maps. In other 
words, where the surface of the ground is between 50 and 
100 feet above the Ordnance datum, there the implements 
will certainly be found. If one goes above the 100 feet line 
the implements become rare, although not absent; for in one 
instance I found an implement near Ealing Dean in gravel 
164 feet above the Ordnance datum. Mr. Evans records the 
finding of an implement 300 feet above the Valley of the 
Darent, in Kent, and 500 feet above the level of the sea; 
Mr. Benjamin Harrison, of Ightham, in Kent, has found 
implements in the valley of a tributary of the Medway, a 
southern affluent of the Thames, at 400 feet above the 
Ordnance datum and 150 feet above the nearest stream; 
and Mr. F. C. J. Spurrell has found an implement near 
Erith, at a height of 175 feet. As a rule, though not 
without exception, it may be considered that the higher the 
implements are found above the Thames-level the more 
ancient they are. In positions removed from a great river 
the height of the nearest stream must always be considered. 
There is no tributary of the Thames near the 164 feet 
position mentioned by me north of Ealing; and it seems 
impossible to avoid the conclusion that the Thames or some 
other river once flowed at that level, and that primaeval man 
made his implements on the elevated terrace. Near where I 
live at Highbury, there is gravel close to “Christ Church” 
at 140 feet above the Thames, and there I recently saw an 
implement disinterred. This high position, clearly, was once 
