642 
rocks by acidulated water, or of rock-salt by springs carrying 
away the brine. Owing to the former cause, falls have taken place 
in several parts of Norfolk, as at Horsford,'^‘ where the Chalk 
has been eroded in pipes or hollows, into which the superincumbent 
strata “ cave in,” or tumble. Mr. A. W. Morant has pointed out, 
that, when the sewage of Norwich was conveyed on to the farm 
at Whitlingham, the land upon which it was discharged was soon 
covered with circular holes, usually from three to five feet in 
diameter, and of various depths ; and on one occasion the ground 
suddenly subsided for a space of twenty-one feet in diameter, 
and to a depth of twelve feet. These were evidently due to the 
“ sand-galls” in the Chalk, and to the washing in of material by the 
excess of water, t 
Heavy rains or earthquakes may promote these falls, just as 
either may promote landslips. The great landslip which took 
place at Lyme Eegis on Christmas Day, 1839, created much 
consternation in the neighbourhood. Volcanoes and earthquakes 
were assigned as the cause, and one individual wrote “ A brief | 
account of the Earthquake,” Avhich Avas published in London, to i, 
shoAV that the phenomenon Avas prophesied in the Eevelations. t 
In September, 1275, the body of the church on Glastonbury { 
Tor was throAvn doAA'n by an “earthquake,” — the toAver alone :J 
remained, and it is there still. I have Avondered Avhether the j 
foundations of the church Avere partially undermined by springs ^ 
carrying aAvay portions of the Oolitic sands on Avhich the church | 
Avas built. This might readily have taken place through the springs 
Avhich issue at the base of the sands Avhere they rest on the Lias. 
It is difficult to understand how an earthquake shock could throAV 
doAvn the nave of the church Avithout upsetting the steeple. 
At Mannington and Briston in Norfolk, small subsidences 
of the land have been recorded ; and I Avas informed that 
Mannington Mere arose from a subsidence that took place in 
1704. In the same neighbourhood two sinkings occurred in 1718; 
one had a diameter of eighteen feet and a depth of nine feet, and 
another a diameter of thirty-three feet and a depth of nearly tAvelve 
feet. These hajApened in a tract of ground Avhere Glacial Sands 
* Arderon, Phil. Trans, vol. xliii. p. 527. 
t ‘ Engineer,’ vol. li. p. 123. 
4 
