242
THE ESSEX NATURALIST.
Shortgrove Park on the north. This road was, no doubt, con-
structed to take the place of the ancient track-way when this,
latter passed out of use. Here, commencing near a bench-
mark on the wall of the park (showing an elevation of 257 feet
O.D.), the track-way and the modern road run parallel, side by
side ; but the track-way is filled so densely with trees and
bushes that its existence is generally overlooked by those who
pass along the road. At this point, the track-way becomes
much shallower, wider and less pronounced. Its northern side.
is now from six to eight feet in height only and very sloping ;
its bottom is from fifteen to eighteen feet wide ; its southern side
lacks any definite bank, but is still bounded by the two parallel
ridges, now from 20 to 25 feet apart, all as in the accompanying
section (text fig. 7). Finally, the track-way having continued
Fig. 7.
rather over half-a-mile, merges into the road to Saffron Walden
close to the Lodge Gate (about 288 ft.) having risen about 130
feet in its course. The road runs on another mile and a half
before reaching the town.
Now, to what cause may we attribute the formation of these
unusual track-ways ?
Apparently, we may look for a geological explanation of their
existence. The chalk hills around Walden are everywhere
covered, to a greater or lesser thickness, by a deposit of boulder
clay ; and it is into this, rather than into the chalk, that these
sunken track-ways are cut. Wherever one of them, descending
a fairly-steep hillside, crosses a spot where the boulder clay
happens to have been deposited thickly, there the pathway
formed by the feet of pack-horses, combined with the action
of the rain-water which trickles down the pathway, has