This two story high needle of dolostone fell like a projectile
pointing down and burying itself deeply. The tilted stratifications
of the rock are clear evidence that it is out of place. From the
Canadian side it is possible to discover the niche in the Lockport
formation from which it fell.
The historical roots of Niagara Falls lie in the Wisconsin
glaciation, which ended some 10,000 years ago. Both the North
American Great Lakes and the Niagara River are effects of this last
continental ice sheet, an enormous glacier that crept across the
area from eastern Canada. The glacier drove through the area like a
giant bulldozer, grinding up rocks and soil, moving them around,
and deepening some river channels to make lakes. It dammed others
with debris, forcing these rivers to make new channels. It is
thought that there is an old valley, buried by glacial drift, at
the approximate location of the present Welland Canal.
After the ice melted back, drainage from the upper Great Lakes
became the present-day Niagara River, which could not follow the
old filled valley, so it found the lowest outlet on the rearranged
topography. In time the river cut a gorge across the Niagara
Escarpment, the north facing cliff or cuesta formed by erosion of
the southwardly dipping (tilted) and resistant Lockport formation
between Lake Erie and Lake Ontario. In doing so it exposed old
marine rocks that are much older than the geologically recent
glaciation.
Three major formations are exposed in the gorge that was cut by
the Niagara River. The Horseshoe Falls, one of the three Niagara
Falls. When the newly established river encountered the
erosion-resistant Lockport dolostone, the hard layer eroded much
more slowly than the underlying softer rocks. The aerial photo
clearly shows the hard caprock, the Lockport Formation (Middle
Silurian), which underlies the rapids above the falls and
approximately the upper third of the gorge wall. It is composed of
very dense, hard and very strong limestone and dolostone.
Immediately below, comprising about two thirds of the cliff is
the weaker, softer and more crumbly and sloping Rochester Formation
(Lower Silurian). It is mainly shale, though it has some thin
limestone layers, and contains large quantities of fossils. Because
it erodes more easily, the river has undercut the hard cap rock and
created the falls.
Submerged in the river in the lower valley, hidden from view, is
the Queenston Formation (Upper Ordovician), which is composed of
shales and fine sandstones. All three formations were laid down in
an ancient sea, and their differences of character derive from
changing conditions within that sea.
The original Niagara Falls were near the sites of present-day
Lewiston, New York, and Queenston, Ontario, but erosion of their
crest has caused the waterfalls to retreat several miles southward.
Just upstream from the Falls’ current location, Goat Island splits
the course of the Niagara River, resulting in the separation of the
Horseshoe Falls to the west from the American and Bridal Veil Falls
to the east.
Although erosion and recession have been slowed in this century
by engineering, the falls will eventually recede far enough to
drain most of Lake Erie, the bottom of which is higher than the
bottom of the falls. Engineers are working to reduce the rate of
erosion to retard this event as long as possible. The Falls drop
about 170 feet (52 m), although the American Falls have a clear
drop of only 70 feet (21 m) before reaching a jumble of fallen
rocks which were deposited by a massive rock slide in 1954.
The larger Canadian Falls are about 2,600 feet (792 m) wide,
while the American Falls are 1,060 feet (323 m) wide. The volume of
water approaching the Falls during peak flow season is 202,000
ft³/s (5,720 m³/s).1,2 During the summer months, when maximum
diversion of water for hydroelectric power occurs, 100,000 ft³/s
(2,832 m³/s) of water actually traverses the Falls, some 90% of
which goes over the Horseshoe Falls. This volume is further halved
at night, when most of the diversion to hydroelectric facilities
occurs.
Lockport Dolomite (Dolostone) is one of the major sedimentary
rocks found in this area. The Dolomite name refers to both a rock
and a mineral. The rock is now more frequently called the
Dolestone. The mineral, Dolomite, is found in the rock. The mineral
is in the carbonate group and is chemically called "Calcium
Magnesium Carbonate." The mineral is seen appearing as a part of
the rock in the picture at left. Dolomites form in marine
environments and, indeed, much of the Lockport area was once under
water. Rock of Dolomite is hard and withstands weathering well. It
was thus a popular choice for home and building construction. It is
also used in the production of crushed stone. The Dolomite stones
can be easily seen along the Niagara Escarpment at Lockport,
especially near the Lockport Locks in downtown. Here the Dolostone
formation is about 75-feet high and was one of the most difficult
challenges for builders of the canal.
Back in 1820 before canal construction, there were no drills
that could penetrate this rock to put blasting powder in it.
However, a temper-hardened drill was especially created for the
purpose by a blacksmith.
Many buildings and homes in the Lockport area were built with
this hard stone removed from the canal and lock dig. Lockport
Dolostone traverses a wide band of the Niagara Frontier.
The majority of minerals found here occur in this rock
formation. Dolostone/Dolomite was also referred to as "Niagara
Limestone" in certain early literature. It is of the Middle
Silurian age. Medium to very dark Grey in color, a freshly broken
surface usually glistens due to many minute cleavages of dolomite.
When struck by a hammer, a strong bituminous odor can be
recognized. Many deep pits and brownish Grey color are the usual
results of weathering.
Lockport Dolomite contains a large number of solution cavities
more or less rounded in shape and from a fraction of an inch to
over a foot in diameter. These are called "vugs" which differ from
"geodes" in that they cannot be easily separated from the main mass
of rock. The minerals are found lining the walls of these vugs,
partly or entirely filling them, or filling cracks and fissures in
the rock.
To log this EarthCache: Your task is to Email me the answers to
these questions.
1. descend 306 stairs to get a photo with the Illegal Alien,
2. tell me how many people are in your group.
3. estimate the size of the rock compared to the others in the
area.
4.Tell me the difference between "vugs" and "geodes"