By the kev. W. Rh. Andrews, F.G.S. 263 
sinks further and further into the solid framework of the land, and 
so it becomes less and less able to change its course. 
Soon side streams bring in their drainage into the main stream, 
and in time there is formed a river with its branches and its tribu- 
taries and streamlets, just as a tree from its trunk divides into main 
branches, and they divide again into smaller ones, and these again 
into twigs. 
In this way a valley originates, and it gradually grows, through 
the action of the running water, that great graving-tool of Nature 
which sculptures the face of the land and produces the harmonious 
diversity of hill and dale. 
The remnants of the plain along which the river first ran still 
exist, for on both sides of the vale we havea range of Chalk downs, 
sloping from west to east. 
Although these two ranges of Downs have suffered considerable 
waste, and are now in parts lower than when they were first elevated 
into dry land, still the central ridges, or lines of highest ground, on 
each side, present us with a slope which we may fairly consider to 
be part of the original slope along which the Nadder first ran. 
On the north side of the district we get continuous relics of the 
original plain, for the central ridge of the Chalk Downs is there 
covered with Clay and Flints for a distance of many miles—showing- 
it to be a surface of some age, and unlike that of the bare Chalk 
hills lying below on either side of it. 
That slope we may see by noticing the gradual fall in the height 
of the downs, when passing from west to east. Looking at the 
heights we find an elevation of 720ft. at the west end of Great 
Ridge Wood, while there is only an elevation of 520ft. at the east 
end of Grovely Wood, showing a fall of 200ft. in ten miles, or 20ft. 
per mile. 
On the south side there are relics of old Gravel with pieces of 
Upper Green Sand Chert along the top of the Downs, and the same 
general fall may be observed as on the northern side of the vale, 
viz., 790ft. at White Sheet Hill, while there is only an elevation of: 
530ft. at the point opposite to the east end of Grovely Wood, thus 
showing a similar slope, 
