CAMERON: SUBSIDENCES OVER PERMIAN BOUNDARY. 345 
pond there ever since. From time to time the sides which are 
of clay, break away and fall in, so that the pond is always hems; 
enlarged. There is no indication of it on the Ordnance Maps ; 
when the Survey was going- on, no noteworthy, if any pond at 
all, existed there. At present there is a large pear-shaped tarn 
stretching neaily across the field, with an outlet on the surface at 
the narrow end. 
Mention has lately been made in the newspapers of a pit, 
that formed eighty years ago at Littlethorpe, and was accompan- 
ied by an explosion, heard at Ripon, fully a mile away. Further 
south by Bishop Monkton, Staveley and Cawthorpe, there are 
more of these pits, all of which doubtless have their history. 
Newspaper reports also have it, that a crack has been heard 
in the vicinity of the Ripon swallow holes, a few weeks ago. 
This being so, the denuding agencies producing the subsidences 
are evidently no more dormant now than formerly. 
In the bed of the Ure below the bridge numerous springs 
bubble up and burst over the surface of the water. These must 
take an important part in the subterranean changes that go on. 
Pits very near the river are perhaps produced by the river 
itself abstracting the limestone, and so undermining the sand- 
stone covering, but there are pits on Copt Hewick Moor in 
sandstone, 150 feet above, and 3 miles from the Ure — measure- 
ments almost too great to admit of the supposition that 
the river had effect in producing them. More likely they are the 
result of surface water falling on the porous and fissured sand- 
stone, where it forms a thin cover to the underlying limestone, 
and entering and honey-combing it as already described. 
The initiative to a number of the pits may have been given 
by the river, at a time when confined between high and overhang- 
ing crags, as it must on^e have been about Ripon, it beat cease- 
lessly against the walls of the narrow gorge, which would become 
caverned and rugged by the force of the torrent. On the boundary 
