to make gunpowder, and saltpetre was one of
the things that had to be carried across the mountains into Kentucky,
until they found it in the hills. No wonder that prospectors went about
looking for nitre beds in the overhanging ledges of rocks along
stream-beds. In such situations the deposits of nitre were found. The
earth was washed in troughs of running water to remove the clayey
impurity. After a filtering through wood-ashes, the water which held the
nitre in solution was boiled down, and left to evaporate, after which
the crystals of saltpetre remained.

Solid masses of saltpetre weighing hundreds of pounds were sometimes
found in protected corners under shelving rocks. It was no doubt in the
fascinating hunt for lumps of this pure nitre that the early prospectors
discovered that the streams which disappeared into the sink-holes made
their way into caverns underground. Digging in the sides of ravines
often made the earthy wall cave in, and the surprised prospector stood
at the door of a cavern. The discoverer of a cave had hopes that by
entering he might find nitre beds richer than those he could uncover on
the surface, and this often turned out to be true. The hope of finding
precious metals and beds of iron ore also encouraged the exploration of
these caves. By the time the war of 1812 was declared, the mining of
saltpetre was a good-sized industry in Kentucky. Most of the mineral was
taken out of small caves, and shipped, when purified, over the
mountains, on mule-back by trails, and in carts over good roads that
were built on purpose to bring this mineral product to market. As long
as war threatened the country, the Government was ready to buy all the
saltpetre the Kentucky frontiersmen could produce. And the miners were
constantly in search of richer beds that promised better returns for
their labour.

It was this search that led to the exploration of the caves discovered,
although the explorer took his life in his hands when he left the
daylight behind him and plunged into the under-world.

Not all lost rivers tell as interesting stories or reveal as valuable
secrets as did those the neighbours of Daniel Boone traced along their
dark passages underground, and finally saw emerge as hillside springs,
in many cases, to feed Kentucky rivers. But it is plain that no river
sinks from sight unless it finds porous or honeycombed rocks that let it
through. The water seeks the nearest and easiest route to the sea. It