192 
RECIPROCATING SPRINGS 
washed out 
loose argilla- 
ceous matters, 
and left the 
limestone 
roof to sup- 
port itself, or 
fall ; as, in 
agent. The rains which have fallen from the remotest times, 
constantly find their way through the chinks of the limestone j 
thus subterranean brooks were formed, which attacked the soft 
argillaceous matter situated under the harder covering of lime; 
stone. This perishable substance was first softened by the wa- 
ter, and afterwards broken down by the currents, which washed 
away the clay and gravel. Inconsequence of this alteration, 
the incumbent rocks of limestone were left to rely on them- 
selves. Such, therefore, fell down as were not supported by 
mutual pressure, while the rest still remain suspended in the 
roof and sides of the caverns, being locked together like the 
stones of an arch. The agents which were formerly em- 
ly have 
streams in 
them. 
have happen - 0 P^ 0 }^ * n excavation of those subterranean chambers, re- 
ed. main, in many instances, to the present day ; for almost every 
cavern is the place of union to a number of secret brooks, 
which enter it in different directions, some of them being pe- 
Caverns most- rennial — but others depend on the weather. The impetuosity 
of these currents is very apparent in some caverns, which are 
filled with water in wet seasons — for the bottoms of them are 
covered with large masses of stone, the edges and angles of 
which are worn away, like those of a pebble that has been 
rolled in the channel of a rapid river. 
Why caves are I have already remarked, that the caves of the North of 
most common- England are commonly found in calcareous strata. This cir- 
iy m calcare- a 7 
ous strata. cumstance may be traced to natural causes — for the rain water 
descends with great ease through the vertical fissures of thesp. 
rocks, which generally rest upon a base of grey schist, and in 
some places on a soft argillaceous substance of a laminated tex- 
ture. This base is not uniformly flat, for it swells occasionally 
into lumps or hillocks, some of which appear above the surround ] 
mg limestone. Such of these hillocks as were originally situ- 
ated under one, or a number of subterranean brooks formed in 
the calcareous strata, have been washed away long ago ; and 
thdf caverns which remain at present, shew the extent and form 
of these demolished eminences. The recesses thus produced, 
frequently contain pools of water ; and if the presence of a 
grotto be necessary to a reciprocating fountain, perhaps few 
places are more ik -ly to produce one, than the neighbourhood 
of Giggleswick. For the country abounds with caves, and 
also with subterranean brooks j one of which is heard very 
distinctly 
