The single factor that makes the Niagara escarpment so unique is
its geology, yet many people who live near it do not know how it
was formed, or even what an escarpment is. The following is a brief
explanation of this fascinating landform.
The Escarpment: Part of a Bigger Picture
is much easier to understand what the escarpment is when you understand
the formation that it is a part of. The Niagara Escarpment is the
cliff face of a ridge that is at the edge of a much larger formation
called the Michigan Basin. The Michigan Basin is a roughly circular
depression in the earth's crust centered under the state of Michigan.
It is formed of layers of sedimentary rock that were created over
420 million years
How Sedimentary Rock is Formed
Michigan Basin used to be the location of an inland sea called the
Michigan Sea. This sea has shrunk and grown in area several times
between 445 million and 420 million years ago (a period of 25 million
the times that this area was under water, the sea was full of life.
The creatures that lived there grew, reproduced, and died, like
modern sea creatures do, and like those modern creatures, their
bodies were left on the floor of the sea after death. Many of these
animals were invertebrates animals without a skeleton. They
may have lacked an inner bone structure, but like most modern invertebrates,
many of them did have hard outer coverings. These were things like
corals, shellfish, trilobites and foraminifers, the descendants
of which can still be found today. Their hard outer coverings were
made of a material called calcium carbonate.
material like this falls to the sea floor, is worn into particles
and forms layers it is called biological sediment. This material
mixed on the sea floor with non-biological sediment: fine material
washed into the sea from rivers, made up of clay, sand and silt.
These layers hardened over time, through the downward pressure of
the overlying material and water, and through both warming and chemical
changes in composition.
with a lot of sand in them became sandstone, which is fairly weak.
Layers with a lot of clay in them became shale, which is also weak.
Layers with a lot of calcium carbonate in them became limestone,
which is strong, or dolostone when magnesium was also present, which
is even stronger.
these layers were laid down along the bottom of the sea floor, these
layers gently tilt upwards at the edges where the old seashore would
have been. The last layers that formed underwater cover a smaller
area than those below them because the sea was shrinking for the
last time. These last layers were formed mainly from clay and sand,
and so are primarily shale and sandstone.
found in escarpment rock. Photo by Madeleine Ernst.
Escarpment is Part of a Cuesta
the perimeter of the Michigan Basin, the edge of the sedimentary
rock layers is tilted upwards. Where this edge is exposed it has
become a ridge formation, also known as a cuesta. Cuestas are ridges
formed by gently tilted rock layers. Every cuesta has a steep slope
where the rock layers are exposed on their edges, called an escarpment.
They also have a more gentle slope on the other side of the ridge
called a 'dip slope'. When you are driving across the Niagara Escarpment
from west to east (try it on Hwy 5 for example) you drive up the
dip slope, and down the escarpment.
are formed for two reasons. One reason is that there are gently
tilted rock layers present. The other is that the layers are of
different hardnesses and so they erode at different rates.
Hill Creek below Albion Falls. Photo by Alan Ernst.
area around the escarpment, where most of us live, has been eroded
by water, wind, frost and glaciation. The cuesta has also been subject
to the forces of erosion, but it is made up of layers of rock that
are more resistant to erosion than the land around them.
In our Niagara Escarpment, the low layers are made up of sandstone
and shale, while the top layers are limestone and dolostone.
of this, the lower weaker layers erode from under top layer, until
the top layer has no support and falls off in large pieces, forming
a cliff face with jumbles of rock at the base. This cliff face
is the Niagara Escarpment!