
- Parr IL. Sect. ii. §.2.] CAVERNS AND TUNNELS. 355 
3. Formation of subterranean channels and caverns.—Measure- 
ment of the yearly amount of mineral matter brought up to the 
surface by a spring furnishes an approximate idea of the extent to 
which underground rocks undergo continual loss of substance. The 
warm springs of Bath, for example, with a mean temperature of 
120° Fahr., are impregnated with sulphates of lime and soda, and 
chlorides of sodium and magnesium. Professor Ramsay has estimated 
their annual discharge of mineral matter to be equal to a square 
column 9 feet in diameter and 140 feet in height. Again, the 
St. Lawrence spring at Loueche (Leuk) discharges every year 1620 
eubie metres (2127 cubic yards) of dissolved sulphate of lime, 
equivalent to the lowering of a bed of gypsum one square kilometre 
(0°3861 square mile) in extent, more than 16 décimétres (upwards of 
five feet) in a century.’ 
By prolonged abstraction of this nature subterranean tunnels, 
channels, and caverns have been formed. In regions abounding in 
rock-salt deposits, the result of the solution and removal of these 
by underground water is visible in local sinkings of the ground and 
the consequent formation of poolsand lakes. The landslips and meres 
of Cheshire are illustrations of this process, In calcareous districts, 
however, more striking effects are observable. The ground may there 
be found drilled with vertical cavities (swallow-holes, sinks, dolinas) by 
the solution of the rock along lines of joint that serve as channels for 
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Fig. 101.—Srcrion or A LimesTONE CavERN (B.). 
11, A limestone hill, perforated by a cavern (b 6) which communicates with the 
valley (v) by an opening (a). The bottom of the cavern is covered with ossiferous 
loam, above which lies a layer of stalagmite (d d), while stalactites hang from the 
roof, and by joining the floor separate the cavern into two chambers. 
descending rain-water. Surface drainage, thus intercepted, passes at 
once underground, where, in course of time, an elaborate system of 
spacious tunnels and chambers may be dissolved out of the solid 
rock. Such has been the origin of the Peak caverns of Derbyshire, 
the intricate grottoes of Antiparos and Adelsberg, and the vast laby- 
rinths of the Mammoth Cave of Kentucky. In the course of time 
the underground rivers open out new courses, and leave their old 
ones dry, as the Poik has done at Adelsberg. By the falling in of 
the roofs of caverns a communication is established with the surface, 
1K. Reclus. “La Terre,” i. p. 340. 
2A 2 
