186 GEOLOGY OF OHIO. 
of the county and of visitors from other States, and deserve a few words 
of description and explanation. As is known to most persons, at Cas- 
talia a volume of water which forms quite a river flows up from several 
deep orifices in the limestone rock, and supplies in its descent to the 
Lake the motive power for several mills. The water maintains nearly 
the same temperature winter and summer, and its flow is more uniform 
than that of surface streams in the vicinity, though sensibly affected 
by periods of unusual and wide-spread drouth. The water of the springs 
is highly charged with lime, rapidly incrusting any object covered by 
it, and it has deposited a sheet of travertine over an area of several 
square miles in the vicinity. The rock in which the subterranean chan- 
nels are excavated, through which the waters of the springs flow, is the 
Waterlime, the uppermost member of the Silurian system. This is a 
magnesian limestone, in fact, a typical dolomite, containing about forty- 
two per cent. of carbonate of magnesia and fifty-five of carbonate of lime. 
This rock forms on the surface an unbroken sheet, reaching from Cas- 
talia to Logan county, the highest land in the State. The true theory 
of the formation of these springs is simply this: the Helderberg lime- 
stone, like many others, is soluble in atmospheric water containing 
carbonic acid It forms the slope of the watershed, and the drainage 
of the country south from Castalia, passing over and through it, has 
dissolved out a connecting system of channels which are really subter- 
ranean rivers. Castalia Springs are formed at the mouth of one of 
these. Similar springs and underground streams are met with in all 
limestone countries. The table-land of central Kentucky affords innu- 
merable examples of them. This plateau is underlain by a thick mass 
of unusually soluble limestone. The surface water dissolves it away so 
easily that it enlarges every crack it penetrates, and has formed a con- 
nected system of underground channels by which all the drainage of 
the country is effected. The celebrated Mammoth Cave is only one of 
these channels. Along the margin of this plateau there are a great 
number of fountains like Castalia Springs, which mark the mouths of 
the subterranean streams that have been described. Such fountains are 
also common in other countries, and the classical Clitumnus bursts out 
at the foot of a limestone mountain, forming a fountain precisely like 
that of Castalia. | 
