File:The Quarterly journal of the Geological Society of London (12684225705).jpg

226
PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .Apr. 7,
Capt. Moody, about 1 920 acres of surface. It at first flows through
a narrow and uncultivated ravine, which, three miles above the small
town of Holmfirth, opens out into a narrow valley. This valley has
always been subject to occasional floods, arising, however, from
natural causes : one of the most disastrous occurred in 1777. The
bottom of the valley shows beneath the turf an accumulation, several
feet thick, of local gravel and rolled fragments of rocks. In some
places debris of this description overlies 2 to 3 feet of imperfect peaty
matter, which again appears to repose on similar detrital accumula-
tions. This drift, however, is much water-worn, and does not seem
to contain any masses of rock at all approaching to the dimensions of
those transported by the late flood.
The following outline map shows the course of the stream and the
situation of the principal places referred to.
Fig. I . — Course of the River Holme and Bigley Stream.
Fig. 2.— (See p. 229.)
Between 1840 and 1844, an embankment 9Q feet high (but which
afterwards subsided to 87 feet), about 480 feet wide at base, 16 feet
at top, and 340 feet in length, was thrown across the valley of the
Digley, three miles above Holmfirth. By this means an artificial lake,
known as the Bilberry Reservoir, about a quarter of a mile long,
300 to 400 feet broad, with a surface of rather more than 1 1 acres,
and in the centre from 70 to 80 feet deep, was formed. It was cal-
culated that, when full, this reservoir held 86,248,000 gallons of
water. The dam was constructed of a wall of clay-puddle, 8 feet wide
at top, and 16 feet at bottom, with a mass of the debris of the valley,
consisting of earth and stones, on either side. The inner slope was
paved with squared stone, and had a base 3 to 1 ; the outer slope, a
base of 2 to 1 .
On the night of the 4th of February last, the giving way of this