bundles of twigs resting upon the dark-brown or black soil of a
previous swamp. Evidently some ancient seekers after health had found
the spring in the swamp, and to make it more convenient to secure the
water had piled brush around it, and then laid down the logs as a
curb. But you inquire, how came the rock, which weighed several tons,
above the logs? The rock was formed by the water. It is composed of
tufa, carbonate of lime, and was formed in the same manner as
stalactites and stalagmites are formed. As the water flowed over the
logs, the evaporation of a portion of the carbonic acid gas caused the
separation of an equivalent quantity of insoluble carbonate of lime,
which, layer by layer, built up the mound. A fragment of the rock
which I possess contains leaves, twigs, hazel nuts, and snail shells,
which, falling from time to time upon it, were incrusted and finally
imprisoned in the stony mass.

[Illustration: SECTION OF HIGH ROCK]

Analysis of a Fragment of the Rock

Carbonate of lime 95.17
Carbonate of magnesia 2.49
Sesquioxide of iron 0.07
Alumina 0.22
Sand and clay 0.09
Organic matter 1.11
Moisture 0.39
Undetermined 0.46
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100.00