Ebbing and Flowing Weil. 38h 
by the following fact; masses of clay, mixed 
with gravel, are found scattered up and down 
these hollows; and as they are lodged in 
chinks from which they cannot be easily re- 
moved by water, I suppose them to be the 
remains of extensive beds, which formerly 
occupied these recesses in the calcareous strata. 
This argillaceous matter, which choaked up 
the natural vaults of our limestone hills in 
early ages, has been gradually worn away by 
a simple, but powerful agent. The rains 
which have fallen from the remotest times, 
constantly find their way through the chinks 
of the limestone ; thus subterranean brooks 
were formed, which attacked the soft argil- 
laceous matter, situated under the harder co- 
vering of limestone. This perishable sub-— 
stance was first softened by the water; and 
afterwards broken down by the currents; 
which washed away the clay and gravel. In 
consequence 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 employed in the excavation of those 
subterranean chambers, remain in many in- 
