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Speaker: Okay, so this is the difference 
between uh, glacial till,

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which is unstratified,

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and non-glacial till.

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So, hopefully you can see 
that this, uh, gravel here

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is well-stratified.

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There are a lot of 
sedimentary features here.

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Um, you can see graded bedding.

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You can also see cross bedding.

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Maybe I can just sort of zoom in on that.

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So there's cross bedding right there.

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Very coarse uh, cross bedding.

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However, the stratification 
or the horizontal layering,

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the general horizontal here,

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indicates that this is not glacial gravel.

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Even though it's approximately 
the correct size

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and sorting distribution.

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The presence of sedimentary features

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as well as, uh, the stratification,

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that's the horizontal layering,

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indicated as not glacial gravel.

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Okay. I'll try and show you
glacial gravel a little later.

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So this is uh, glacial till.

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It is gravel that is deposited 
by a glacier.

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Um, and the identifying
characteristics of it

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is well-rounded clasts,

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however they're not
really really well-rounded.

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They are definitely rounded 
to some extent.

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Um, oftentimes there are striations 
on each individual clast,

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maybe I can show you that later.

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Um, those are scratches that are produced

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when gravel bounces or scrapes against

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other pieces of gravel or the bedrock.

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And the other identifying characteristic

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is that the gravel itself 
is unstratified.

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There is no layering, 
no horizontal stratification.

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Um, and there really are 
no sedimentary features here,

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other than the lack 
of sedimentary features,

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which indicates that 
it was deposited by a glacier.

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Now hopefully you'll be able to see,

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if it'll focus on that,

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the scratches 
on the surface of this clast.

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Those parallel scratches 
are glacial striations,

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which are present on a clast.

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It's stuck in there pretty hard. Argghh.

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It won't come out.

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And in addition to the lack of uh, 
sedimentary features,

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um, one of the characteristics 
that you always look for

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is a very very poor degree of sorting

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in terms of clast size.

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And so, maybe I can 
zoom in on that a little bit.

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You've got clasts of all different, 
uh, sizes.

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Very poorly distributed.

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I suppose even down to these sizes,

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which have fallen down 
from the cliff face, I suppose,

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the gravel face anyways.

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Very poor sorting.

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Okay. Since we're talking about till,

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I thought I'd show you 
what happens when till, um,

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becomes a rock, when it becomes 
consolidated or indurated.

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This is called tillite, which is uh,

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the rock, I suppose, from glacial till, 
a conglomerate.

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This one is very old.

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It is on the side of 
the Trans Canada, here. [cars going by]

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As you can tell by the traffic.

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And it is south of
Wawa in Ontario, Canada.

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[traffic in background]

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This particular crop has been 
highly metamorphosed,

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so these in the Canadian shield.

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Um, so strongly metamorphosed.

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And this tillite is uh, 
weathering very rapidly

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as a result of the intense metamorphism,

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which has caused cracks and fractures

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which increase surface area, of course,

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and cause weathering to accelerate.

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[traffic in background]

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Now realize I'm looking at a shadow here,

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but hopefully you can see 
that the clasts are well-rounded.

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Very poorly sorted, 
in terms of size distribution.

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And are not layered.

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They are unstratified.

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I just thought you might want to see 
what's on the other side of the road.

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That is Lake Superior,

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about an hour south of Wawa, Ontario.

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Pretty big lake, eh?

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Kind of looks like the ocean.

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You can't see the other side 
of Lake Superior,

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even though we're way the heck up 
on the roadside.

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There you can see down to the beach.

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Alright, that's it.

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Bye for now.