session 1904-1905. 
lxiii 
the Greensand. The face of the pit was “ honeycombed ” by the 
nests of sand-martins which a workman stated had arrived during’ 
the preceding week. On the opposite side of the line, north of the 
station, the ground is a little higher, and the highest part is capped 
by a bed of gravel and sand (now being removed for road-metal and 
garden paths), containing boulders apparently derived from the 
higher part of the Greensand, which has here been eroded away, 
and also rocks of foreign origin drifted from Palaeozoic beds in the 
north. 
Descending into the valley of the Plit, other sections of the 
Woburn Sand were seen, and the party then divided, the walkers, 
under the guidance of Mr. Saunders, crossing Plitwick Moor to 
Plitton and Wardhedges Quarry, and the cyclists, conducted by 
Mr. Hopkinson, taking the road through Greenfield and Plitton to 
the Castle Hill, Clophill. 
Mr. Saunders reports : “ The walking party visited the source of 
the Plitwick mineral springs. Most of the members tasted the 
water, which had been filtered, and it was found to be strongly 
impregnated with iron and vegetable acids. It has powerful 
medicinal properties, chiefly tonic and astringent. After passing 
Greenfield Mill the course led by the side of the River Plit. It 
was noticed from the appearance of the water that it contained iron, 
which was being deposited on the pebbles in the brook. It was 
very unlike the bright, sparkling streams which pass through the 
Chalk district of the south of the county.” Mr. A. E. Gibbs adds : 
“ The works are prettily situated in the midst of a plantation of 
birches, and are surrounded by well-kept gardens where the 
daffodils were flowering profusely. In the Sphagnum -moss of the 
bog that curious insectivorous plant, the round-leaved sundew 
(Drosera rotundifolia), was found in abundance. The animal life 
proved equally interesting, the common lizard (Lacerta vivipara ) 
being seen basking in the sunshine, and the green tiger-beetle 
(Cicindela campesiris ), with its short, rapid, jerky flight, rising on 
every side as the party walked through the herbage.” 
On their way to Castle Hill the cyclists visited Plitwick Quarry, 
where the “Carstone” of the Lower Greensand is exposed. This 
is on a higher horizon than the Woburn Sand, and, like it, shows 
current-bedding. The section at Castle Hill exposes the same and 
the succeeding beds to the highest portion of the Greensand seen in 
this neighbourhood. It is of special interest, as it shows 10 feet of 
dark-coloured clay, called by the workmen “black clay” to 
distinguish it from the “blue clay” of the Gault, occurring in 
three distinct beds of about equal thickness with thin layers of sand 
between them, dark-red carstone being above the clay, and light- 
coloured sand beneath it. This black clay occurs at Shefford, to 
the east, where it has thinned to one foot, but it is not known to 
occur elsewhere. It is used by the workmen at the brickfields at 
Lower Gravenhurst, which would have been visited had time 
permitted, to mix with the clay obtained there from the Lower 
Gault. The face of the quarry in which the layers of clay are 
