HERTFORDSHIRE NATURAL HISTORY SOCIETY. 
xlvii 
Field Meeting, 4th June, 1887. 
RICKMANSWORTH. 
Sections exposed in making the new line of railway from Pinner 
to Rickmansworth were examined by the Society in June, 1886.^ 
The London Clay and Woolwich and Reading Reds were then seen, 
and the line was left near Moor Park before it crosses the valley of 
the Colne. On the opposite side of this valley the Chalk has been 
cut into, and this meeting was originally arranged to enable the 
members to examine sections of the Upper Chalk thus exposed. It 
was found, however, towards the end of May, that the cuttings in 
the Chalk were no sooner completed than they were covered up 
with a layer of soil on which grass was destined soon to grow, and 
the programme had to be altered. Although the route now chosen 
was not, perhaps, so interesting geologically as that which had to 
be abandoned might have been, it had the advantage of being more 
picturesque. 
The meeting, as last year, was held in conjunction with the 
Geologists’ Association, and was under the direction of Mr. 
Hopkinson. Prom Rickmansworth (London and North-Western) 
Stationf members of the two Societies crossed the fields to 
Woodcock Hill Kiln, halting on the way on the summit of a hill, 
260 feet above sea-level, from which was obtained a view of the 
valley of the Colne, and of the junction with it of the subsidiary 
valleys of the Chess and Gade. 
This hill, the Director stated, owes its existence to the bed of 
gravel seen upon it. The top, as usual with hills of chalk (as 
well as hills of clay) capped with gravel, is flat, and there is a 
steep slope towards the valley of the Colne and a gentler slope 
in other directions. This conformation is due to the preserva¬ 
tion from subaerial denudation of the gravel-covered portion of 
the hill, the rain falling upon it percolating through the gravel 
without washing it away to any considerable extent, whereas 
outside the margin of the gravel the rain washes away the chalk, 
or, by the carbonic acid it contains, chemically dissolves it, and 
this more rapidly towards the valley than towards the higher 
ground behind the hill; the steep slope being formed by the 
resistance to denudation of the edge of the bed of gravel, which, 
however, would gradually give way by the undermining of the 
chalk. Towards the west another similar gravel-capped hill was 
seen, the steep edge, showing the extent of the gravel, being 
distinctly apparent. This gravel is of doubtful age, but certainly 
as old as Middle Glacial, similar gravels, of which the beds covering 
these two hills seem to be portions, elsewhere running under 
boulder-clay. 
A few minutes’ walk brought the party to "Woodcock Hill Kiln, 
where sections of the Woolwich and Reading Beds and of the 
basement-bed of the London Clay were seen. As these sections 
* See ‘ Trans. Herts Nat. Hist. Soc.,’ Yol. IY, p. xvii. 
f The Metropolitan Station was opened in September. 
