[Episode 1 Preview: Geology]
>> NICK EYLES: The Land Between is actually
unique geologically in Ontario, because you
have this remarkable transition from the Shield
rocks to the north.
This is a metamorphic rock, by which we mean
it’s been subjected to great heat and pressure.
And if you look at the mineralogy in the rock,
it tells us that it was forming at least twenty
kilometers underground.
And by underground, we mean deep beneath high
mountains called the Grenville Mountains.
And they would have been bigger than today’s
Himalayas.
So in walking over this surface, we are actually
looking at the roots of these deep mountains.
And we’ve lost at least twenty kilometers
of rock.
By and large the surface that we see on the
southern margin of the Shield is much the
same as it was eight hundred million years
ago.
But as you come to south off the Shield - as
you drop down in elevation, you get on to
the leading edge of the limestones.
And these are the remains of ancient seafloors
- about 450 million years ago.
And if I pick up a piece of the limestone,
I can see it’s full of fossils.
This is referred to as a ‘bioclastic limestone,’
where the entire rock is made up of the remains
of fossils.
And just here in The Land Between the limestone
is completely devoid of soil.
As we go further south, they become thickly
covered.
And it’s possible the ice was moving sediment
to the south, slowly stripping whatever sediment
was here - but also there’s been a lot of
melt water running across these surfaces.
And it’s probably washed these completely
clean of sediment.
And in some places you see the actual contact
- where limestone is resting right on the
Shield, and that’s called an unconformity.
And there’s many hundreds of millions of
years that are lost between the formation
of the Shield, and the first sedimentary rocks
that are deposited on top.
So it’s only in this very narrow strip,
where you actually see this junction between
two worlds.
