LOWER LEVELS
(LEVELS E & F)
The phreatic tubular passage
from Great Relief Hall leads down to River Hall at Mammoth Cave's level
E. This room provides the easiest access down to see the modern
underground rivers at the water table (level F). River Hall is the lowest
point on the “Historic tour”. The "River Styx tour" continues
down from River Hall to see the water table (albeit from a distance).
River Hall (looking N) - the walls
& ceiling of this room have prominent scallops (phreatic flow-dissolution
features). This room is at the junction of two tributaries of an old
underwater river system. One tributary brought water from the River Styx
area, and the other brought water from the passage leading from Great Relief
Hall. The ceiling & uppermost walls consist of basal Fredonia Member
limestones (Ste. Genevieve Ls.). The middle to lower walls and floor are
all upper St. Louis Limestone ( Meramecian Stage, Middle Mississippian),
specifically the Horse Cave Member of the St. Louis Ls.
River Hall - beautifully scalloped
ceiling of River Hall, formed when this room was flooded.
River Hall - dissolution features
along the walls of River Hall have complex geometries. They are the
result of complexly intersecting small & large solution pockets. The
rocks are Horse Cave Member limestones of the St. Louis Ls.
Dead Sea - this pool represents the
level of the modern water table in Mammoth Cave (level F). During
rainstorms or winter snow melting, the water table here can be much
higher. After such events, the water table lowers again, but leaves mud
behind. Mud covers the rocks & passages around the Dead Sea and the
River Styx. The tourist trails in this vicinity are frequently slippery
from wet mud. Sometimes, River Hall (see above) has been close to being
flooded.
A waterfall can be heard
from this overlook at the Dead Sea. The sound of rushing water comes from
the nearby Charon's Cascade.
Dead Sea - rills (vadose dissolution
features) are present along the edges of Dead Sea. These are either mud deposits or mud-covered
limestones. The bedrock in this area is part of the Horse Cave Member of
the St. Louis Limestone.
Scallops - beautiful small-scale
scallops developed on a St. Louis Limestone bed (trailside, Dead Sea-River Styx
area). The wet mud coating indicates relatively recent flooding at this
level.
Scallops - interestingly dimpled St.
Louis Limestone walls in the Dead Sea-River Styx area.
Solution Pocket - scallops, solution
pockets, and other karst forms are abundant along passage walls in the Dead
Sea-River Styx area. The rock is Horse Cave Member of the St. Louis
Limestone.
Mud-Filled Solution Pockets - the water table at level
F fluctuates up & down with the passing of surface rainstorms and
wintertime snow melting. Here's some solution pockets in the St. Louis
Limestone that have been secondarily filled with modern fluvial mud. The
mud is cohesive enough to remain in the cavities. Some of the mud filling
has been subsequently sculpted (partially eroded) by more recent water movement
during floods.
Karstified St. Louis
Limestone - wet mud coats these interestingly-shaped dissolutional features
called pendants in the Dead Sea-River Styx area. They are similar
to those in River Hall - complexly intersecting solution pockets. Some
surface karst on Bahamian islands has a similar chewed-up, “swiss-cheese”
appearance.
Rapier's Pit (looking from below) - a
nice domepit along the southwestern side of the River Styx. Domepits are
vadose dissolution features. The rocks are still St. Louis Limestone
(Horse Cave Member).
Echo River is a moderately
long, somewhat snaking underground river at Mammoth Cave's level F. Its
top surface represents the elevation of the modern water table. Early
tours routinely included boat rides on Echo River (see photos from old
postcards below). Such experiences are a thing of the past (sad,
sad). Rocks along the walls & ceiling of Echo River are Horse Cave
Member limestones (St. Louis Ls.). A fossiliferous chert horizon (Lost
River Chert Bed) also occurs at or below the water table here (I've not seen
it, so I can't comment on its nature from first-hand observation).
Echo River - early boat tour at level
F in Mammoth Cave. The background (ceiling & distant walls) has been
artistically enhanced (= fake).
Some unusual organisms live
below the water table in Mammoth Cave. They evolved from
surface-dwelling ancestors into blind (eyeless) creatures with translucent
bodies (no pigment). They include cavefish (Amblyopsis
spelaea and Typhlichthys
subterraneus) and various arthropods (Orconectes
pellucidus, Palaemonias ganteri,
Caecidotea
spp., Crangonyx spp., Stygobromus spp.).
Waters in the Echo River and
River Styx drain through flooded passageways and emerge at the land surface at
two springs on the southeastern side of the Green River.
River Styx Spring
Echo River Spring