Geological Society of London. 143 
In the case of the Shode valley, only beds below the contour-level 
of 350 feet in its upper part, and of 800 feet or less in its lower 
part, can be referred to the former action of the Shode, and those 
above this belong to a high-level drift of uncertain age. The com- 
position of the various gravels was described in detail. 
The implements are found on the surface of the land at all levels 
up to 600 feet, and Mr. Harrison has discovered them at 40 localities 
in the hydrographical basins of the Shode, the Darent, the Ley- 
bourne stream, and in part of the Thames basin. Two groups of 
implements extend far beyond the limits assigned to the river-drifts 
formed since the present hydrographical basins were established, and 
must be accounted for by some other means than those in connection 
with the former régime of the existing streams. A description of the 
_ general characters and variations observable in the implements was 
given. It is evident from the condition of most of the implements, 
that they have been imbedded in some matrix which has produced an 
external change of structure and colour. In the case of the river- 
gravel sites, the question presents no difficulty. Three classes of 
implements have been found—(i.) where the flint still shows some of 
its original colour; (1i.) those of which the surface has turned from 
black to white, has been altered in structure, and acquired a bright 
patina, and which shows no trace of wear ; (iii.) those of which the 
flint has also lost its original colour, but has been stained, and is 
with or without patina; these are generally much rolled. The 
characters of the first call for no comment. Those of (ii.) and (iii.) 
are very marked, and there is no difficulty in referring each to a dis- 
tinct matrix. The implements of class ii. have been embedded in a 
stiff brick-earth, generally of a reddish colour, and those of class iii. 
seem to have lain in ferruginous beds of sand or gravel. Reasons 
were given for supposing the surface to have been once covered with 
a deposit of clay or loess, since denuded except where preserved in 
pipes, and that a continuous plane descended from the high range 
of the Lower Greensand to the Thames valley, which has since been 
lowered 300 feet or more. It was also shown that the high-level 
deposits were formed anteriorly to the Post-glacial drifts of the 
Medway and Thames Valleys. It is probable that the loess is a 
deposit from flood-waters, and that some of it may be referred to the 
Medway flowing at a higher level ; but the highest deposits cannot 
be so accounted for, and the author referred to the possibility of 
glacial action, without insisting on it. ‘The deposit on the Chalk- 
plateau is abruptly cut off by the river valleys, and the rudest forms 
of implements, such as those of Ash and Bower Lane, occur on this 
plateau at from 500 to 550 feet, and the author thinks they may 
possibly be of Pre-giacial age. The changes which have taken place 
in the physiography of the district, and the great height of the old 
chalk-plateau, with its clay-with-flints and southern drifts, point to 
long intervals of time, and to the great antiquity of the rude im- 
plements found in association with these drifts. That the removal of 
the material indicates the existence of agents of greater force than 
those operating under the present river régime closes up the time 
