342 CAMERON : SUBSIDENCES OVER PERMIAN BOUNDARY. 
SUBSIDENCES OVEE THE PERMIAN BOUNDARY BETWEEN 
HARTLEPOOL AND RIPON. BY A. G. CAMERON, OF H.M. 
GEOLOGICAL SURVEY OF ENGLAND AND WALBS. 
My attention having- been drawn to the numerous forms of 
shrinkage of the land, peculiar to the trend of the Permian 
boundary between Hartlepool and Ripon, the following paper 
contains some remarks on these and other subsidences, which 
have a common origin in denudation, by the action of under- 
ground waters circulating in the strata. 
At Ripon, the top of the Permian is marked by a number of 
conspicuous holes or pits in the land, extending down to consider- 
able depths into the rocks beneath. 
Between Sutton-Howgrave and Ripon, there are not less than 
50 of these pits, ponds and hollows, in a distance of 4 miles ; some 
of these subsidences have taken place within the past ten years, 
others since the Ordnance Survey of the district, while some 
remain, of which no record can be obtained. Very interesting 
accounts of the " Ripon Natural Pits " have been given by the 
Rev. J. S. Tute of Markington, in Geol. Mag., Vol. v., page 178, 
and in a paper read at Wakefield at the seventy-third meeting of 
the Geol. and Polyt. Soc. of Yorkshire. 
The top of the Permian first enters the land at Hartlepool, 
where the Slake is a large " hollow or sinking in the ground." 
Adhering to the trend of this boundary are numerous pools, 
ponds, swamps, and dry peaty hollows, whose configuration 
appear due to the superficial deposits, settling down into cavities 
or cauldrons in the rocks on which they rest. Such are the " Hell 
Kettles " at Croft, Hall Garth, Blackheath, and Queen Mary's 
Dubbs, near Ripon, and tarn-shaped depressions holding accu- 
mulations of black earth, just north and south of Bedale. 
The Ripon swallow holes, some of which are said to have once 
been 200 feet across, and 80 to 100 feet deep, have been attri- 
buted to the dissolving away of gypsum or sulphate of lime, or to 
