XIV 
PROCEEDINGS, 
A good collection of fossils was made by the party, whose 
examination of the sections exposed was brought to a sudden 
termination by heavy rain which compelled a hasty retreat to 
the Swan Hotel, Leighton, for tea. 
Field Meeting, 11th April, 1908. 
MIMMS HALL AND POTTERELLS PARK. 
The object of this meeting was to examine the swallow-holes 
in the Mimms Hall Brook under the direction of Mr. W. 
Whitaker, F.B.S., F.G.S., and in conjunction with the 
Geologists’ Association, the party assembling at Potter’s Bar 
Station. 
To Mimms Hall the walk was over the London Clay and 
Beading Beds, and over these formations a stream flows from 
the south. There the underlying Chalk is encountered, and, 
owing to its porous nature and the lowering of the plane of 
saturation, the water has made for itself channels in it, called - 
swallow-holes, down whibh it passes, and although it sometimes 
reappears lower down the stream it is eventually lost to its 
own river-bed and probably finds its way into another drainage- 
area, the valley of the Lea, except on very rare occasions when 
the Chalk is saturated up to its bed, when it flows on and 
becomes the main source of the Eiver Colne. 
The first swallow-holes seen were at a bend in the stream 
about a third of a mile north of Mimms Hall. Water was 
pouring down these, but they did not take it all, some being left 
to sink into a small hole at the next sharp bend of the stream, 
a little further north. Here a sample of the water was taken, 
an analysis of which will be found in the ‘ Proceedings of the 
Geologists’ Association’ (vol. xx, p. 503). For the fine set of 
swallow-holes at Water End, so called because formerly the 
water usually ran to that point, there was none left. This was 
of course also the case at the finest group of all, in Potterells 
Park, where the ground is riddled with them over a considerable 
area ; but at North Mimms, between Water End and Potterells 
Park, they were found to be taking in sewage from the cottages, 
a method of disposing of which ought not to be permitted. 
The walk was continued to Welham Green, whence most of 
the party drove to Hatfield and had tea at the Salisbury Hotel. 
The writer visited the locality about a fortnight before this 
meeting and found the road under water near Water End, the 
stream having overflowed its banks, and it continued to flow so 
far as Potterells Park, where all disappeared. 
These swallow-holes are more fully described in a paper on 
“ The Biver Colne and the Swallow-holes at Potterells ” read at 
our field meeting on the 19th of April, 1890, and printed in our 
' Transactions ’ (Vol. VI, pp. xxix-xxxii). 
