Bolton Notch State
Park: Squaw Cave
The Bolton Range (as used by Michael Bell,
1985) stretches from the Middletown area northward into
Massachusetts. It has two significant breaks: the
Connecticut River flows through one break; the other break is
Bolton Notch (Leary, 2004, p.109). The Notch was eroded by
glacial melt-water that flowed eastward (Stone and others, 2005)
through a fault and fracture zone. In the process it exposed
westward dipping (tilted) meta-sedimentary rocks, including a layer
containing appreciable carbonate minerals. This is noteworthy
because carbonate minerals are relatively soluble in rainwater and
groundwater. This EarthCache is about one of the results of
soluble rock layers: caves. Caves are dark
inside: you may want to bring a flash-light.
Purpose: This EarthCache is
published by the Connecticut Geological and Natural History Survey
of the Department of Environmental Protection. It is one in a
series of EarthCache sites designed to promote an understanding of
the geological and biological wealth of the State of
Connecticut.
Location: Squaw Cave, Bolton
Notch State Park,
CT
N41o47.358’, - 072o26.774’
PARKING LOT
Directions:The east end of Interstate
384 runs through Bolton Notch. Entrance to the park is off
the west-bound lane of I-384 about 0.2 mi west of the Rte
44-Rte 6 merge. The entrance has no sign and thus difficult
to find. If you look carefully you can see the stop sign for
cars leaving the parking area.1 The turn is very
sharp: almost 180o in a very narrow
space. Caution: turning (right) off I-384 into the
entrance drive to the parking lot can be somewhat hazardous because
of the fast moving traffic. The GPS location
given here is for the parking lot.
The parking lot is next to a linear greenway
that follows an old railroad grade (New York and New England Rail
Road). The trail to the west and north (left out of the
parking lot) heads toward Valley Falls Park in Tolland. To
the east (right out of the parking area) the trail passes through a
tunnel beneath I-384, to Andover and beyond. The Notch is a
gap in a more-or-less continuous ridge-line: the Bolton Range.
The Notch owes its formation to faults with
their associated fractures and to glacial melt-water at the end of
the last ice age. The Bolton Range is underlain by schist and
quartzite with minor marble/calcareous gneiss. The schist and
quartzite are resistant to glacial abrasion and hence stand up with
a higher elevation than surrounding areas, especially higher than
the less resistant sedimentary rocks to the west in the Connecticut
River Valley. The range has moderate to local very steep slopes and
even cliffs. The range is broken at Bolton Notch by at least
one and possibly several faults of small displacement. The
faults provided planes of weakness that glacial melt-water
exploited. The melt-water stream
1. If you miss the turn exit the highway at the Rte-6 exit
(to Manchester) and immediately make a u-turn in the space
provided. This will put you back on the highway going
east-bound. Immediately get into the left lane and exit left
onto Rte-44. After going under the bridge make a u-turn in
the space provided and get back on I-384 going west and try
again. At the following web-site a trail map may be found
that also shows the highway configuration:
http://www.boltonnews.org/boltonnotchstatepark.html
flowed eastward through the notch according to
Stone and others (2005). The melt-water may have come off ice
west of the notch or perhaps drained a temporary lake just west of
the notch. At any rate, the melt-water stream carved a
250-foot deep notch through the range (ridge top just north of the
Notch is 820+’ whereas a benchmark in the Notch has an elevation of
583’).
The notch exposes geological
formations2 that dip (are tilted) toward the
northwest at about 30o. The rocks that we will see
on this EarthCache are mica schist, calcareous gneiss (marble in
places), and staurolite schist. The calcareous gneiss
contains carbonate minerals
(calcite or dolomite) that are soluble in
groundwater. Many dissolution features, including a small
cave may be found where this rock crops out.
Activity 1. Find the
following location: N 41o47.412’
-072o26.786’ ( +12’). To get there you
will follow the old rail bed east (right from the parking area)
toward a tunnel. Just before you get to the tunnel go up a
trail to the left. This will bring you to the busy highway
(I-384) where appropriate caution is needed to stay out of
harm’s way. When you get to the highway notice the rocks
on your left (Figure 1a; these rocks are covered by
bittersweet and grape vines in the summer and are difficult to
spot. The picture below was taken in the spring-time).
The rock contains many small holes of various shapes.
Fractures are enlarged.
a.
b.
Figure 1. a. Rocks at base of cliff
adjacent to highway. Note the many holes in the rock.
This is a clue that the rock contains soluble components.
b. Picture of cliff face taken from across the highway during
the early spring. Figure 1a shows rock at lower left of this
picture. Cave may be seen about mid-cliff level on the right
side of the picture just to left of telephone pole closest to the
right edge of the picture. The cave appears as a dark shadow
in the middle of the outcrop.
The rock has a slight yellowish-rust
color. The rust color indicates that minerals in the rock
containing iron have been weathering, probably dissolving.
The holes are further evidence for dissolution of some of the
minerals in the rock. This rock layer is exposed higher on
the cliff face the farther east you go.
Continue walking off the road until the
guard-rail ends; there you find a trail that heads steeply up the
slope (it may be concealed by grape and bittersweet vines during
the
2. An account of the geology of Bolton Notch State Park may
be found at the following website:
http://www.ct.gov/dep/cwp/view.asp?a=2716&q=325116&depNav_GID=1650
summer and early fall). At the top of
the steep slope will be a cliff face that contains a cave in the
same layer that we saw down by the highway. This should put
you at the coordinates above.
There is poison ivy around the cave entrance,
particularly to the right. Be careful if you are
sensitive.
a
b.
c.
d.
Figure 2. a. Picture of
entrance to Squaw Cave. b. Inside Squaw cave.
Notice that when we took the pictures we omitted some familiar
object that would give the reader a sense of scale. That will
be your job in order to log this EarthCache. c.
Fractures are enlarged by dissolution. A 5” pen is barely
discernable just to the right of the right limb of the “V”
gash. d. Close up of the weathered surface of the
calcareous gneiss.
This is one of the few caves in Connecticut
formed by dissolution of the rock. Most caves in Connecticut
are formed by rocks that have fallen upon or lean against another
rock to form a cave beneath. These we call shelter
caves3. Connecticut does not have a lot of
soluble rock, such as limestone or marble. Marble crops out
in Western Connecticut and many of the caves known from that part
of the state formed by dissolution of marble.
Limestone and marble are both composed of
carbonate minerals, calcite or dolomite, which are soluble in
acidic water. Rainwater is slightly acidic4
and when it seeps through the soil, it leaches organic-soil acids
that enhance its acidity. When acidic rainwater (or
groundwater) seeps into the rock it dissolves soluble minerals,
such as carbonate minerals. Water slowly trickles through the
rock in fractures; hence, it is not by coincidence that fractures
are enlarged. Indeed, the cave formed by enlargement of a
fracture. This can be can be seen in the ceiling of the
cave. At the apex you can see a fracture running the length
of the cave. At times water seeps from the fracture and may
collect on the floor of the cave during wet seasons.
Legend has it that the daughter of a Podunk
Indian chieftain, Wunnetumah, and her colonist-husband, Peter
Hager, lived in the cave for a time before he was
killed5.
Activity 2. N.
41o47.419’, -072o.26.887’. To get to
this location retrace your path back toward the parking lot but
continue westward (along the old railroad grade) a few yards past
the parking lot until you find a trail that goes steeply up the
hill to your right. Continue on this trail until it
forks: take the right fork to the above location; a
yellow-blazed trail to the left, called the Mohegan Trail, takes
you a 1.3 mile loop that returns to the old railroad grade a little
farther to the northwest. You will scramble over several
small outcrops of gray to silvery garnet-bearing staurolite schist
(Figure 3 a, b) before coming to a large outcrop that overlooks the
highway below. Schist is a metamorphic rock that was
recrystallized and reformed several kilometers below the earth
surface where the temperature was several hundred degrees.
The rock originally may have been a shale of some sort. The
high pressure and temperature caused the original minerals to react
with each other and with the fluids in the rock to form a new rock,
in this case schist. Schists are micaceous rocks that lack
significant compositional banding (for contrast, look at the
distinct layers that comprise the calcareous gneiss in Figure
2d). Certainly the rock has a grain to it which is called
schistosity, a type of metamorphic foliation.
At the outcrop overlooking the highway,
light-colored pegmatite (Figure 3c and Figure 4) has intruded into
the staurolite schist. The pegmatite consists of quartz,
potassium-feldspar, and muscovite mica. The mineral grains
that make up the rock are very coarse-grained; many are greater
than a centimeter in diameter. It is an igneous rock that
formed when molten material intruded into the preexisting
metamorphic schist. The metamorphic foliation is deformed
(Fig. 4) near the intrusive contacts. Possibly the intrusion
process
Figure 3. Schist and pegmatite.
a. Loose piece of staurolite schist along trail to activity 2
location. Schist is silver-gray color (caused by tiny
muscovite micas in the rock) with inch-long crystals of black
staurolite. Small garnet crystals are visible on some parts
of the schist (see just to right of keys). The shiny
silver disc is 2” (~5 cm) in diameter
3b. Loose piece of garnet
schist. Garnet crystals are about 0.5 mm in diameter.
One small staurolite crystal is visible in right-center of
picture.
3c. Pegmatite at activity
2 location. Green color applied by anonymous
graffiti-artist. White mineral grains that make up the rock
are feldspar. Gray glassy mineral is quartz. Muscovite
mica is present also. Pegmatite is a course grained igneous
rock (once molten); its mineral grains are measured in
centimeters. By contrast, granite has a similar composition,
but the mineral grains of granite rarely exceed 2 or 3
millimeters.
caused the deformation. In some places,
however, small faults can be identified adjacent to the deformed
schist. In these locations, the deformation may be related to
the faulting rather than the intrusion.
The pegmatite lacks metamorphic foliation;
thus its intrusion postdated the last metamorphic event in this
area. It is likely that the pegmatite formed about 275 m.y.
ago.
A.
B.
Figure 4. Pegmatite
(light-colored rock on which most of the graffiti has been painted)
intruded into schist (Activity 2 location). A. Layers
of schist on right are tilted toward the observer whereas layers of
schist in center of image are standing nearly vertical. The
deformation may be related to the intrusive process.
B. An outcrop of schist is shown on right and on left
a coarse-grained pegmatite. Quartz separates the pegmatite
from the schist. The quartz is slightly rusty colored and
contains fragments of schist. It likely formed along a
fault. Faults may be responsible for the deformation of the
schist in this and other locations near the pegmatite.
To get credit for this EarthCache:
Answer the following questions and provide two
images of yourself or members of your group: 1) in the cave
noting the height of the individual so that the size of the cave
can be estimated by the image viewer, and 2) at the overlook on the
pegmatite showing the highway below.
Question 1: What is the measurement of
the widest part of the entrance to Squaw Cave?
Question 2: Which of the
following three events occurred first and which occurred last (most
recently)?:
a. intrusion of pegmatite
b. formation of cave
c. metamorphism of shale and
limestone to schist and marble.
Difficulty: 1
Terrain Rating: 3.5 (steep slopes)