36 
H. G. FORDHAM—ON BOULDERS 
direction, but not in depth or extent , the valleys of the Glacial 
Period; but it seems clear that there has been a considerable amount 
of denudation since that period, and that not only have the clays 
been washed away from a large portion of the face of the country, 
but also that the valleys have been greatly deepened. If this were 
not so, we should find here and there traces and patches of clay low 
down in, and probably even at the bottom of, some of the valleys. 
In some places, no doubt, there is a sort of washing of clay in the 
valleys; but it appears to have resulted from the washing down of 
the clay which lies on the tops of adjacent hills. The chalk hills, 
where free from boulder-clay, have a very slight subsoil; in the 
area of the outcrop of the chalk-with-flints this is a dark mould 
with flints; on the lower beds the subsoil is marly.*' 
It should also be noted that where patches of gravel and clay lie 
on the tops of the hills, they are generally found in slight depressions 
of the chalk; perhaps their preservation is partly due to this fact, 
although it may be that these depressions have been formed by the 
decay of the underlying chalk and the consequent letting down of 
the superincumbent clays and gravels subsequently to the period 
at which they were originally deposited. 
On referring to Mr. Elsden’s map at p. 151 of Yol. II of our 
1 Transactions/ it will be seen that there are marked upon it two 
considerable outlying patches of boulder-clay on the If. W. side of the 
railway between Baldock and Royston. It is from the smaller and 
more northerly of these two patches that the boulders now lying 
in and near the village of Ashwell have been obtained. This patch 
lies on a hill which forms the prominent terminal mass of one of 
the transverse ridges I have already referred to. This hill, known 
as Clay Rush Hill, is at its highest point 329 feet above sea-level. 
No doubt a considerable quantity of gravel has been obtained from 
it. When roads were made and mended exclusively with local 
materials, the glacial gravels in this district were largely drawn 
upon for road-metal; and in the course of digging for gravel, when 
* A small pit (B on map) cut in the slope of a hill, on a by-road on the 
south side of and a quarter of a mile from the main road from Baldock to 
Royston, in the parish of Therfield, shows :—(1) Blackish sub-soil full of angular 
fragments of chalk with a few flints, a few inches to three feet in thickness ; (2) 
Chalk, a good deal broken, containing many broken Inocerami , generally small 
( ? mytiloides ), and occasionally a small round or finger-shaped flint. Towards the 
north end of the pit a sand-pipe is shown, containing fine, red and yellowish loam. 
There are traces also of ferruginous matter in cracks in other parts of the section. 
There is, however, no trace of loam in the subsoil, which lies directly on the 
chalk and cuts across the top of the sand-pipe. On the hill above, angular 
fragments of flint are numerous, and amongst them are large flints almost un¬ 
broken. A shallow pit (A on map) about half a mile north-west of this section, 
and on a lower bed of the chalk, j ust north of the railway, gives a section three to 
four feet deep, in the bottom of a shallow valley, as follows:—(1) subsoil, eight 
inches to one foot; (2) yellowish marl, containing small fragments of angular 
blue and white flints, and much small chalk rubble, varying in thickness up to 
one foot two inches; (3) a similar bed to 2, but with much flint (about one- 
third of the bed), in angular pieces (none worn), of varying size up to six inches 
and eight inches in longest diameter, and with here and there a small boulder- 
clay pebble, about one foot in thickness. 
