Central Florida is a limestone region with its drainage largely
subterranean and in part below the level even of the sea. Sink
holes are common, and many of them are occupied by lakelets. Great
springs mark the point of issue of underground streams, while some
rise from beneath the sea. Silver Spring, one of the largest,
discharges from a basin eight hundred feet wide and thirty feet
deep a little river navigable for small steamers to its source.
About the spring there are no surface streams for sixty miles.

THE KARST. Along the eastern coast of the Adriatic, as far south
as Montenegro, lies a belt of limestone mountains singularly worn
and honeycombed by the solvent action of water. Where forests have
been cut from the mountain sides and the red soil has washed away,
the surface of the white limestone forms a pathless desert of rock
where each square rod has been corroded into an intricate branch
work of shallow furrows and sharp ridges. Great sink holes, some
of them six hundred feet deep and more, pockmark the surface of
the land. The drainage is chiefly subterranean. Surface streams
are rare and a portion of their courses is often under ground.
Fragmentary valleys come suddenly to an end at walls of rock where
the rivers which occupy the valleys plunge into dark tunnels to
reappear some miles away. Ground water stands so far below the
surface that it cannot be reached by wells, and the inhabitants
depend on rain water stored for household uses. The finest cavern
of Europe, the Adelsberg Grotto, is in this region. Karst, the
name of a part of this country, is now used to designate any
region or landscape thus sculptured by the chemical action of
surface and ground water. We must remember that Karst regions are
rare, and striking as is the work of their subterranean streams,
it is far less important than the work done by the sheets of