xliv 
PROCEEDINGS OE THE 
it is quite as rare to find tliis sandstone in position as it is to find 
our Hertfordshire conglomerate. 
The conglomerate is here seen to he split up into blocks, showing 
that it has been subjected to considerable disturbance, either by 
subsidence or upheaval, after its consolidation, and the hardness 
and durability of the siliceous cement is evidenced by the splitting 
of the pebbles in the general lines of fracture. In some places 
the pebbles have become so soft that they may be cut with a 
knife, while the matrix preserves its hardness. Another point of 
interest is that here and there the surface of the conglomerate is 
seen to be smooth and rounded, as if it had been subjected to the 
action of ice. It is the only rock we have anywhere in this neigh¬ 
bourhood, and probably the only rock in our Tertiary basin, which 
is sufficiently durable to show any trace of glacial action. 
A careful examination of the conglomerate was then made in 
different parts of the pit, and pebbles here and there were freely 
subjected to the action of pen-knives, a few being found which 
could be cut into. The splitting up of the conglomerate was 
observed, and its surface was seen to be in some places evidently 
worn by attrition. The beautifully-white fine sand seen reposing 
upon an unconsolidated portion of the pebble-bed also attracted 
attention. 
On leaving Newberries the road leading to Boreham "Wood was 
taken for a short distance, and, turning off it towards Letchmoor 
Heath, a stream flowing out of Elstree Reservoir into the River 
Colne was crossed. The bed of this stream is frequently dry; it 
was so when crossed lower down on the way to Newberries four 
years ago, and there was not much water in it now, but the prox¬ 
imity of the underground reservoir, the plane of permanent satura¬ 
tion in the chalk, to which attention was soon to be directed, was 
evident from a stream of water running down the road, which was 
not merely surface-drainage from the recent rain, its source being 
beneath the surface. 
The route was now past Kendall Hall and then past Kendall 
Pound, between which place and Battler’s Green the principal 
“ swallow-holes” in the district are to be seen, there being others near 
Letchmoor Heath and Bushey. On arriving at the Battler’s Green 
swallow-holes no water was to be seen. There having been a long 
period of dry weather the recent rainfall would be speedily absorbed; 
but that sometimes a large quantity of water would be seen to 
disappear was evident from the amount of solid matter which had 
been carried away. 
The following explanation of the occurrence of these swallow- 
holes was then given by the director. 
The average yearly rainfall in this part of Hertfordshire for the 
last 20 or 25 years may, he said, be taken roughly as 26 inches. 
Of this amount scarcely a quarter, or 6^ inches, sinks through the 
soil, by far the greater portion being evaporated or absorbed by 
vegetation. The water which sinks through the soil ultimately 
finds its way to the rivers, usually appearing above the surface in 
