24:^ The A)iierican Geolotjisf. April, 1895 
size. Crevices liave also been opened by the contraction of 
the sediments. These crevices and fault planes acted as clian- 
nels for meteoric waters, and were enlarged by them. The 
period succeeding the deposition of the Ozark rocks was one 
of great erosion. This is indicated by the small representa- 
tion of the Upper Silurian antl Devonian rocks, the country 
not being submerged during the greater portion of the time 
these rocks were being deposited elsewhere. The presence of 
organic acids in the meteoric waters would increase their sol- 
vent action.- There was, moreover, much erosion after the 
deposition of the Lower CiirboniFerous rocks, and also after 
the deposition of those of the ( 'oal Measures. That there was 
a slight dei)osit of these latter rocks over a large portion of 
southern Missouri, is probable. Tlie area was above water, 
however, from an early date, in theC'oal Measure period, with 
a possible slight exception, to the present day. The cavities 
of the large southwestern deposits were formed by this solvent 
action of surface waters which enlarged joint planes and 
crevices. Their location on tlie margin of the Coal Measures 
afforded opportunity for the access of waters carrying large 
(juantities of organic acids, derived from decaying vegetation, 
which increased their solvent power materially. Added to 
this, the structure of the rocks of the Lower Carboniferous, 
pure limestone with many intercalated chert beds, furnished 
material readily dissolved, as well as contact planes affording 
easy access to the material. It may be readily conceived that 
once the limestone supporting these beds of chert dissolved, 
that chert, on account of its extreme brittleness, would frac- 
ture and break into the materials which now forms the breccia 
that characterizes these deposits. 
Horizontal cavities. Hat tabular-shaped spaces enlarging 
into cliambers at times, such as are frequently met with in 
the southeast, had their origin in the same solvent action of 
water, here localized among certain stratification anil joint 
planes where the rock yielded more readily to that action. 
Those cavities, the filling of which have given us the type 
known as "circle deposits," are best explained by referring to 
certain caves which have their opening in the roof. One of 
these caves in Stone county was examined and surveyed by 
Dr. E. O. Hovej' and the writer. The main feature was a 
