UNDERGROUND WATER 141 
this action caves may be formed; and as the water 
flows along, constantly receiving tributaries, a maze of 
underground caverns may result, as is so well illus- 
trated in the noted Mammoth Cave of Kentucky 
(Fig. 68), and the caverns of Luray in Virginia. 
These channels may be occupied by actual sub- 
terranean rivers, 
draining into 
ike 
some surface | wmowe 
stream which 
they enter in the : 
form of springs. itn 
Limestone strata ~~ 
| nr 
: 
nora AVENUE 
<< 
SY RIT 
aii 
en La 
are often honey- 5 ae 
combed by these pie 
caverns. The |* ec B sone 
water of the : 
surface drains 
Fre. 68. 
Map to show maze of subterranean channels in 
towards a saucer- Mammoth Cave region. 
like depression 
or sink-hole. In the centre of this it sinks into the 
earth to commence its underground journey, which may 
be many miles in length. Such rivers, as well as per- 
colating water, are enlarging the caves by solution ; 
but some of the greater streams of the subterranean 
passageways, are also deepening the caves by mechani- 
cal wear of erosion. 
