G43 
rest on Glacial Marl. And tho sinkings were attributed by 
Mr. P. Le Neve, who described them, to springs carrying away 
quicksand.* 
At Bristol!, in 1788, two holes were formed by .subsidence, in 
a similar tract of ground ; one M'as sixty feet in diameter with a 
depth of twenty-seven feet, and the other was ninety feet in 
circumference, t These sinkings, as well as those at Mannington, 
may have been partly aided by dissolution of the Chalk beneath 
the Glacial Drift ; but the explanation given by Mr. Lc Neve is 
well worth consideration, and it accords with some suggestions 
I made on the loAvering of the level of a country by subterranean 
denudation in my paper on the ‘ Scenery of Norfolk.’ 
Artificially, subsidences have been produced by mining exca- 
vations, and they have sometimes occun’cd at Norwich and other 
parts of Norfolk by the breaking in of tho roof of an old gallery 
driven into the Chalk. 
One might conclude that it is unwise to build one’s house on 
a calcareous rock, or on a porous soil overlying it. On the 
contrary, sand is considered an excellent foundation, when it 
occupies some extent of ground, maintains a thickness of about 
ton feet, and is itself based on a firm foundation ; for it accom- 
modates itself to a weight, and is not so yielding as clay. 
P.S.— Strange to say, since this paper was communicated to the Society, 
we have been disturbed by an earthquake, which manifested unusual energy, 
and must rank as one of the most serious on record in this country. 
Originating at Colchester, it extended as far as Norfolk, having been felt 
in a feeble form at Lynn, Fakenham, Norwich, Diss, and Yarmouth. I 
hope to contribute some particulars of this earthquake at a future meeting 
of the Society.— II. B. W. 
PhU. Trans, vol. xxx. p. 766. 
t Gentleman’s Mag. vol. Iviii. p. 649. 
