HERTFORDSHIRE NATURAL HISTORY SOCIETY. 
XXXY11 
lying to the south by the stream now flowing at a much lower 
level. Referring to specimens he had brought with him, collected 
from various parts of this county and Buckinghamshire, he pointed 
out that only here and near North Minims was the pudding-stone 
found in immediate contiguity to the Reading Beds, while elsewhere 
extending beyond Missenden in the west it was found embedded in 
drift gravels, clay, or clay-with-flints. With regard to the con¬ 
glomerate itself, great variation in the composition of the inclusions 
and the matrix was shown. Some specimens partook more of the 
nature of a breccia than a conglomerate, and while the inclusions 
in some, notably those under review, consisted almost entirely 
of pebbles of the Reading Beds, in others angular and subangular 
fragments of flint and chert, with rolled pebbles of chalk and clay 
silicified, were largely present. 
Passing on to the question as to the origin and mode of formation 
of these blocks, the Director expressed the opinion that they were 
of fluviatile origin and formed at the debouchure of streams flowing 
northward, which, draining the London Clay, cut through the 
Woolwich and Reading Beds, and deposited the detritus either in 
subterranean streams or in the bed of a pre-glacial river having 
a course parallel to and south of the Chalk escarpment. The two 
remaining representatives of these northern streams were the 
Mimms stream, flowing from South Mimms, which only after 
heavy rains flowed into the Colne, disappearing at other times, on 
reaching the Chalk, through various swallow-holes, and the Med- 
burn stream, flowing from Aldenham Reservoir also into the Colne, 
the swallow-holes near Radlett, through which the greater part of the 
stream formerly disappeared, having now been plugged. The silica, 
subsequently cementing these re-arranged materials, he considered 
to have been derived from the decomposition of the soluble silicates 
of the felspathic constituents of the Glacial Drift. Time would 
not allow of a further development of his views on this question, 
but he hoped to embody them, on some future occasion, in a detailed 
paper on the subject. 
Field Meeting, 30th July, 1890. 
PARK STREET, ST. ALBANS. 
On this occasion the members of the Society and their friends 
were invited to tea by Mr. F. W. Silvester, of Hedges, St. Albans, 
and also to visit the Frogmore Flower Show held at his residence. 
The proposed walk by the River Yer, announced in the circular 
for this meeting, was abandoned, and the members, numbering 
about thirty, went direct to the Flower Show, where several 
collections of wild flowers and grasses, from the neighbourhood, 
gathered and arranged by children, and a fine collection of named 
specimens of herbaceous plants used in the preparation of medicine, 
shown by Mrs. Baldwin, Munden Lodge, Bricket Wood, attracted 
special attention. 
