OCCURRENCE OF CHALKY BOULDER CLAY AT CHINGFORD. 3 
last, I noticed some half dozen bushes of Clematis vitalba growing 
jiwt below the crest of the hill, on the slope facing the Lea Valley, 
a new locality to me for the plant ; and the idea of a possible 
local patch of Boulder Clay again recurred to my mind. No 
•section was available, but a steep bank beneath some trees 
afforded an opportunity to dig a shallow hole, when what seemed 
to be Chalky Boulder Clay was soon in evidence ; it. consisted 
of tough brown clay with embedded fragments and pebbles 
of white chalk. 
A later visit to Yardley Hill, armed with a spade and the 
necessary permission from the Forest Superintendent (whose 
courtesy I here gratefully acknowledge), enabled me to dig a 
trial-hole, 20 yards distant from the bank mentioned, and 
2ft. bin. deep, which proved very stony brown clay (probably 
for the most part derived from the local London Clay) containing 
rounded chalk fragments : the included stones being chiefly 
flint, with many rounded flint-pebbles, a few quartz, quartzite 
and sandstone pebbles, and small calcareous concretions and 
ironstone concretions. I found also one small pebble of Car¬ 
boniferous Limestone, containing a recognisable Produdus. 
The surface of the ground is very much broken by slips of 
the hill-side, as is usual on clay slopes, and may have been further 
disturbed by shallow surface diggings for gravel or marl. 
This new patch of Boulder Clay is probably of very small 
extent, perhaps not 100 yards each way. Its exact position 
is at the very extremity of the ridge of Yardley Hill, just below 
the crest of the hill, and on its western or Lea valley slope, at 
about 200 feet above O.D., and some 150 feet above the floor 
of the Lea valley. 
The nearest point in the Lea Valley where Chalky Boulder 
Clay has hitherto been mapped is at Monkham Hill, one mile 
north of Waltham Abbey, and four miles distant northwards 
from Yardley Hill. The new locality is four miles distant from 
the patch of Boulder Clay at Enfield, five miles from that at • 
Bell Common, Epping, and a like distance from the patches at 
Theydon Bois in the Roding Valley, and at Chigwell Row. 
It is the most southerly patch of Boulder Clay in the Lea Valley, 
and probably represents the final effort of the Great Ice Sheet 
at or near its southernmost margin. 
I may add that an inspection of the neighbouring locality 
