The Giant Sleeps Today
Sleeping Giant State Park, Hamden CT
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.
Supplies: You will need a copy of this earthcache writeup
to answer the questions once on site. Spoilers may be included in
the descriptions or links.
Directions:
From I-91: take Exit 10. Then get onto Route 40 connector and
stay on until the end. At the light, take a right onto Route 10N
drive 1½ miles then take a right onto MT Carmel Avenue. The park
entrance is on the left across from Quinnipiac University.
From Wilbur Cross Parkway: take Exit 61. Go north onto Whitney
Avenue for 3 miles and take a right onto MT. Carmel Avenue. The
park entrance is on the left across from Quinnipiac University
From I-84 to Cheshire: take Route 70S onto Route 10 south drive
5 miles. Then take a left at the light onto MT. Carmel Avenue. The
park entrance is on the left across from Quinnipiac University.
There is a parking fee ($7) on weekends and holidays.
N41o25'16.12", W72o53'55.95"
Quick description: Have you ever walked on a Sleeping
Giant? Local folklore tells of an ancient Indian Chief who over
indulged eating oysters and offended the spirits. A spell was cast
upon the Chief while he slept never to awake. Sleeping Giant is one
of the state's most recognizable land formations and located in the
Mount Carmel section of Hamden.
The rocks exposed at Sleeping Giant State Park were formed
between 225 and 200 m.y.a, (million years ago) during the late
Triassic and early Jurassic Periods of the Mesozoic Era. The most
abundantly exposed rocks in the park are igneous rocks that formed
by solidification of once molten rock called magma (when magma is
erupted onto the surface of the earth it is referred to as lava).
During late Triassic and early Jurassic time, Connecticut was
located in the middle of a large super-sized continent called
Pangaea. Pangaea was destined to break apart into smaller
continents, many of which closely resemble those of today. During
the early phases of the breakup of Pangaea, Eastern Connecticut was
mountainous and central Connecticut and portions of western
Connecticut were lowlands in which sedimentary rocks accumulated.
By the beginning of Jurassic time layers of sedimentary rock had
accumulated to a thickness of 1-2 km (miles?) in the Sleeping Giant
State Park area.
As the breakup continued, great fractures developed in the
crust. By the onset of Jurassic time one or more of the fractures
extended deep enough to tap into magma that had formed in the
mantle, 60 or more kilometers (miles?) beneath the surface. Magma
rose through the fractures to the surface of the earth forming
fissure eruptions and extruding an extensive lava flow. Magma in
the fractures solidified after the eruption forming a long network
of dikes that extend northeastward from southern Connecticut into
Maine and Canada. Evidence for three such igneous events can be
found in Connecticut and other east coast regions.
The earliest volcanic event started about 201 m.y.a. when magma
rose through a set of fractures that extended from Branford, CT,
through Stafford and northeasterly into Canada. A line of volcanoes
was created. Lava of basaltic composition flowed from those
volcanoes into the low areas of central and western Connecticut.
One to two kilometers below the surface the rising magma oozed
horizontally near the base of the older sedimentary rocks forming
intrusive sheets of magma. When the magma cooled it solidified into
basalt or diabase. Sleeping Giant is one such sheet, as are the
Barndoor Hills in Simsbury and East Rock and West Rock in New
Haven.
When magma cools, individual minerals begin to crystallize. If
the rate of cooling is rapid, magma rapidly by formation of many
small crystals. If the rate of cooling is slow, fewer crystals form
but grow to a larger size. The rate of cooling is a function of how
rapidly heat can escape from the magma.
Magma of basaltic composition that cools rapidly to a
finely-crystalline rock is termed basalt by geologists. One
that cools more slowly and has medium-sized crystals is termed
diabase (or dolerite)1. Magma of
basaltic composition that cools even more slowly and develops
larger crystals (2-3 mm inches or feet?) is called
gabbro.
1. Basalt and diabase are called trap-rock and form the
prominent ridges and mountains (including Talcott Mountain, Meridan
Mountain, Lamentation Mountain, and the Sleeping Giant to name but
a few) in the central part of Connecticut. Trap-rock is an
important resource of Connecticut. It is crushed and used for
numerous construction purposes. Connecticut ranks with the top
mining states in the nation (based on tonnage) because of the
trap-rock extraction industry.
Magma that intruded into the cooler sedimentary layers at
Sleeping Giant initially cooled rapidly. Thus, fine-grained basalt
is found on the top, bottom and around the edges of the intrusion.
The magma cooled slower in the middle of the intrusion and formed
diabase.
Since the time of intrusion of the sheet of magma into the
sedimentary layers, the entire central region of Connecticut has
been tilted eastward by earth-forces and subjected to the ravages
of weather, glaciers and erosion. What we see today are the eroded
edges of sedimentary rock layers and part of the intruded sheet of
igneous rock. Millions of tons of rock material have been eroded
away during the millennia. In some places of Sleeping Giant Park we
can see the part of igneous rock that cooled adjacent to the cooler
sedimentary rock and is finely crystalline. It appears relatively
smooth on a broken surface. In other places we see igneous rock
from the middle of the intrusion. It cooled slowly and developed a
medium-grained texture typical of diabase. Mineral crystals are 1-2
mm in length and the surface looks rough and blotchy.
ACTIVITY 1. Obtain a trail guide from a park attendant
(on-line link) and find a trail that will take you to
N41o25'50.19", W72o53'26.06". Look at the
rock outcrops in that immediate area. The rock surfaces are
weathered to a brownish color (freshly broken rock is black or
dark-greenish gray) but the texture of the rock is still
observable. Is it finely-crystalline or
coarsely-crystalline?.basalt or diabase? Knowing that can you infer
whether the rock crystallized close to it's contact with the older
and cooler sedimentary rocks or was more to the interior of the
intrusive sheet where it would have cooled (and crystallized)
slowly?
Look for the rock in the photograph which was taken on the trail
south of the tower. Notice the weathering rind. This area has
little or no glacial soil covering it and the rock has been
directly exposed to the elements for about 17,000+ years
(see discussion for activity 3 below). Note how the weathering
tends to round off the sharp edges and corners of the rock making
it more rounded. This is typical of the weathering of even-grained
igneous rocks and is referred to as spheroidal weathering.
On the up-hill hike to the location for activity 1 you pass a
large smooth rock outcropping exposed in a small gully between the
upper and lower trail at a switchback (hairpin curve). The outcrop
is on your right (N 41o25'48.1", W
072o53'34.3") several yards past the intersection of the
Tower Trail with the red-triangle trail.
The outcrop slants down toward the lower path at about
30o and has been used by some hikers as a short-cut
between the uphill and downhill part of the switchback on the Tower
Trail. 
If you did not notice it on the hike
to ACTIVITY 1 location, look to the left after the first
prominent switchback on your way down. The rock is weathered
to the typical brownish color. Notice that there are a couple
of long shallow (0.5-1. mm deep) grooves gouged in the rock
(see photograph). They are near horizontal. The grooves do not
expose fresh rock, although they most likely did when they
were formed. The grooves have been subject to the same amount
of weathering as the rest of the rock and are therefore as old
as the exposed-surface of the rock. During the last Ice Age,
glacial-ice at least a kilometer thick covered this part of
Connecticut. Ice that is thicker than about 120 m. becomes
unstable at it's base and deforms by slowly flowing as a
mechanism to make itself thinner and more stable. The ice was
thicker to the north, reaching up to 8 km thickness in
northern Canada. Ice flowed across the state of Connecticut in
a general south-easterly direction. Local obstacles may cause
slight deviations from that general direction.
Ice flowage is not a smooth procedure especially at the base of
the ice. It likely flows in fits and starts and scrapes across the
earth surface. Soil and rock fragments of all sizes get frozen into
the bottom of the ice and act as abrasion agents on the underlying
bedrock. This is much like sandpaper does to wood over which it is
worked. Large particles, such as cobbles and boulders, frozen into
the base of moving ice creates gouges and scratches in the
underlying rock. They are called glacial striations and are a
direct indication of orientation of the ice flow: i.e. it
must have been parallel to the length of the striation. Fine
particles, such as soil and mud, frozen into the base of ice smooth
the rock surface.
About 20,000 years ago global warming led to melting of the
glaciers. Naturally it warmed more to the south than to the north.
The warm temperatures began melting ice at its southern terminus,
which at greatest extent was along Long Island. The southern edge
of the ice progressively melted; about 17,500 years ago it was
situated along the coast of Connecticut. Although the melting
continued the remaining ice moved forward in a general
south-easterly direction. When the ice melted, all the debris
frozen into it was left on the ground, forming a deposit we call
glacial till. The soil that covers the rock outcrop at Sleeping
Giant is from glacial till.
ACTIVITY 2. Toward which direction did the base of
the glacier move when it created the striations at N
41o25'48.1", W 072o53'34.3"? An exact
measurement is not needed for the purposes of this exercise. Look
at the till. It is an approximation of the composition of the
debris frozen into the base of the glacier. Is it composed more of
coarse particles that would cause gouges or more of fine particles
that would tend to smooth the rock surface or both?
ACTIVITY 3. Compare the weathering of the surface of the
striated rock seen here (N 41o25'48.1", W
072o53'34.3") with the rock exhibiting spheroidal
weathering seen at the activity 1 location. Can you form a
hypothesis to explain why the rock with the striations did not
develop a weathering rind like the rock exhibiting spheriodal
weathering seen at the activity 1 location? (This is an extra-point
question.)
To log this EarthCache: Answer the questions, and provide
a photo at the site and number in group.
Additional information and references:
The Sleeping Giant Park Association web site: www.sgpa.org
http://dep.state.ct.us/stateparks/parks/sleepinggiant.htm has
the CT DEP information for Sleeping Giant State Park.
Bell, Michael, 1985, The Face of Connecticut: Hartford,
Connecticut Geological and Natural History Survey, Bull. 110, 196
p.
Flint, R.F., 1962, The surficial geology of the Mount Carmel
Quadrangle. Connecticut Geological and Natural History Survey,
Quad. Rept. 12, 25p
Fritts, C.E., 1963, Bedrock Geology of the Mount Carmel
Quadrangle. U.S. Geol. Surv. Map GQ-199.
McHone, Greg, 2004a, Great Day Trips to Discover the Geology
of Connecticut. Wilton, CT, Perry Heights Press, 206p.
McHone, J.G. 2004b, Connecticut in the Mesozoic World.
Connecticut Geologic and Natural History Survey, Spec. Pub. 1,
40p.
How do people log this EarthCache? People will need to
provide answers to the first two EarthCache activity questions and
send an image of themselves at the top of the tower at the Activity
1 location.
Difficulty: 3,4
Terrain: 1 maybe 2 - involves 1.6 mile hike up an
improved trail that is wheel-chair accessible.
Type of land: State Park
EarthCache category: Igneous intrusion; glacial
feature
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