Concerning the Subcarboniferous, or Mississippian Series in Part I.,
Vol. IV., Missouri Geological Survey, Dr. C.R. Keyes says: "In the great
interior basin of the Mississippi the basal series is exposed more or
less continuously over broad areas, extending from northern Iowa to
Alabama, and from Ohio to Mexico."

While this broadly extended series of limestone is honey-combed in many
places and all directions by wonderful caverns, those of the Ozark
regions in Missouri, although comparatively little known, are well worth
knowing, and are possibly the most ancient limestone caves in the world.
Of the region in which they occur, Dr. Keyes, in the volume last quoted,
says: "The chief typographical feature of the state has long been known
in the Ozark uplift, a broad plateau with gentle quaquaversal slopes
rising to a height of more than one thousand five hundred feet above
mean tide, and extending almost entirely across the southern part of the
district. On all sides the borders of this highland area are deeply
grooved by numberless streams flowing in narrow gorges. Against its
nucleus of very ancient granites and porphyries the Ozark series of
magnesian limestone was laid down. Then the area occupied by these rocks
was elevated, and around its margins were deposited successively the
other members of the Paleozoic. The Ozark region was thus the first land
to appear within the borders of the present state of Missouri." He
further says: "Although it has long been known that the Magnesian
Limestones are older than the Trenton, and that they lie immediately
upon and against the Archæan crystallines unconformably, their exact
geological age has always remained unsettled. There seems to be but
little doubt, however, that part of the series is equivalent to the
Calciferous of other regions. It is also pretty well determined that
certain of the lower beds, all below the 'Saccharoidal' Sandstone
perhaps, are representatives of the Upper Cambrian or Potsdam. These