GENERAL GEOLOGY.



of the Kentucky survey as the Cumberland Sandstone. After
this the floor of the sea was sparingly peopled with life, dur-
ing the whole of the Clinton and Niagara epochs, when it was
probably deep water. This deep sunken condition of the ocean
floor continued in the D)evonian time, when this section seems
to have been the seat of a deposition such as is now going on
beneath the Sargassa Sea of the Atlantic of to-day. The de-
caying sea-weed and other orranic matter made a bed from three
hundred feet thick along Lake Erie to forty feet thick in South-
ern Kentucky, averaginmg about one hundred feet in Kentucky.
This bed furnishes the rich lubricating oils of the Cumberland
Valley. After this came again shallowe water, and quick succes-
sive sand-invasions moving from the north, which formed sev-
eral hundred feet of beds. These beds probably represent but a
fraction of the tim-e required to form the Black Shale which lies
below. This part of our section is called the Waverlv, and is
commonly regarded as being more nearly related to the Carbon-
iferous than to the Devonian series of rocks. After this period
came a repetition of subsidence, and a cessation of -he sand-
invasions. During this time there was such a development of
sea-lilies or stemmed Echinoderms, that this time deserves to
be called the period of crinoids. This accumulation ranges in
depth from a few feet along the Ohio River to five hundred or
more feet under the Western Coal-field. It marks a period of
tolerably deep still water, filled with lime-secreting animals. It
is probably to the unbroken character of this succession of life,
and especially to the crinoids with their upright stems, that we
owe the uniformly massive character of many of the beds of this
Subcarboniferous Limestone.
  Next in the ascending series we come on the coal-bearing
rocks. Their deposition was begun by the sudden shallowinig
of the water over this region, bringing the old sea-floor near the
surface of the lowater, and subjecting it to alternating invasions
of sand borne by stron- currents, and exposures in low-lying
flats covered by a dense swaamp vegetation. Each of these
swvamp-periods answers to a coal-bed; each recurring subsi-
dence, to the deposits of sands and shales that lie between
the coals.



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