WEBVTT

00:00:05.967 --> 00:00:12.671
Speaker: Okay, so this is the difference 
between uh, glacial till,

00:00:12.671 --> 00:00:14.573
which is unstratified,

00:00:14.573 --> 00:00:16.924
and non-glacial till.

00:00:16.924 --> 00:00:21.248
So, hopefully you can see 
that this, uh, gravel here

00:00:21.248 --> 00:00:23.333
is well-stratified.

00:00:23.333 --> 00:00:26.053
There are a lot of 
sedimentary features here.

00:00:26.053 --> 00:00:31.090
Um, you can see graded bedding.

00:00:31.090 --> 00:00:33.243
You can also see cross bedding.

00:00:33.243 --> 00:00:36.996
Maybe I can just sort of zoom in on that.

00:00:36.996 --> 00:00:39.633
So there's cross bedding right there.

00:00:39.633 --> 00:00:43.719
Very coarse uh, cross bedding.

00:00:43.719 --> 00:00:47.506
However, the stratification 
or the horizontal layering,

00:00:47.506 --> 00:00:49.442
the general horizontal here,

00:00:49.442 --> 00:00:53.529
indicates that this is not glacial gravel.

00:00:53.529 --> 00:00:55.864
Even though it's approximately 
the correct size

00:00:55.864 --> 00:00:59.402
and sorting distribution.

00:00:59.402 --> 00:01:01.705
The presence of sedimentary features

00:01:01.705 --> 00:01:04.762
as well as, uh, the stratification,

00:01:04.762 --> 00:01:06.380
that's the horizontal layering,

00:01:06.380 --> 00:01:09.718
indicated as not glacial gravel.

00:01:09.718 --> 00:01:13.438
Okay. I'll try and show you
glacial gravel a little later.

00:01:13.438 --> 00:01:16.958
So this is uh, glacial till.

00:01:16.958 --> 00:01:20.445
It is gravel that is deposited 
by a glacier.

00:01:20.445 --> 00:01:25.349
Um, and the identifying
characteristics of it

00:01:25.349 --> 00:01:30.421
is well-rounded clasts,

00:01:30.421 --> 00:01:34.392
however they're not
really really well-rounded.

00:01:34.392 --> 00:01:37.812
They are definitely rounded 
to some extent.

00:01:37.812 --> 00:01:41.248
Um, oftentimes there are striations 
on each individual clast,

00:01:41.248 --> 00:01:43.166
maybe I can show you that later.

00:01:43.166 --> 00:01:46.271
Um, those are scratches that are produced

00:01:46.271 --> 00:01:48.706
when gravel bounces or scrapes against

00:01:48.706 --> 00:01:51.242
other pieces of gravel or the bedrock.

00:01:51.242 --> 00:01:52.827
And the other identifying characteristic

00:01:52.827 --> 00:01:56.814
is that the gravel itself 
is unstratified.

00:01:56.814 --> 00:02:01.569
There is no layering, 
no horizontal stratification.

00:02:01.569 --> 00:02:04.755
Um, and there really are 
no sedimentary features here,

00:02:04.755 --> 00:02:07.425
other than the lack 
of sedimentary features,

00:02:07.425 --> 00:02:11.579
which indicates that 
it was deposited by a glacier.

00:02:11.579 --> 00:02:14.164
Now hopefully you'll be able to see,

00:02:14.164 --> 00:02:16.217
if it'll focus on that,

00:02:16.217 --> 00:02:21.088
the scratches 
on the surface of this clast.

00:02:21.088 --> 00:02:26.444
Those parallel scratches 
are glacial striations,

00:02:26.444 --> 00:02:32.299
which are present on a clast.

00:02:38.031 --> 00:02:40.821
It's stuck in there pretty hard. Argghh.

00:02:42.770 --> 00:02:44.472
It won't come out.

00:02:44.472 --> 00:02:49.243
And in addition to the lack of uh, 
sedimentary features,

00:02:49.243 --> 00:02:54.348
um, one of the characteristics 
that you always look for

00:02:54.348 --> 00:02:57.135
is a very very poor degree of sorting

00:02:57.135 --> 00:02:59.904
in terms of clast size.

00:02:59.904 --> 00:03:04.624
And so, maybe I can 
zoom in on that a little bit.

00:03:04.624 --> 00:03:09.546
You've got clasts of all different, 
uh, sizes.

00:03:09.546 --> 00:03:14.284
Very poorly distributed.

00:03:14.284 --> 00:03:20.425
I suppose even down to these sizes,

00:03:20.425 --> 00:03:26.096
which have fallen down 
from the cliff face, I suppose,

00:03:26.096 --> 00:03:29.351
the gravel face anyways.

00:03:29.351 --> 00:03:31.503
Very poor sorting.

00:03:31.503 --> 00:03:33.355
Okay. Since we're talking about till,

00:03:33.355 --> 00:03:36.825
I thought I'd show you 
what happens when till, um,

00:03:36.825 --> 00:03:41.312
becomes a rock, when it becomes 
consolidated or indurated.

00:03:41.312 --> 00:03:45.115
This is called tillite, which is uh,

00:03:45.115 --> 00:03:49.687
the rock, I suppose, from glacial till, 
a conglomerate.

00:03:49.687 --> 00:03:52.573
This one is very old.

00:03:52.573 --> 00:03:56.977
It is on the side of 
the Trans Canada, here. [cars going by]

00:03:56.977 --> 00:03:58.995
As you can tell by the traffic.

00:03:58.995 --> 00:04:03.701
And it is south of
Wawa in Ontario, Canada.

00:04:03.701 --> 00:04:08.206
[traffic in background]

00:04:08.206 --> 00:04:12.793
This particular crop has been 
highly metamorphosed,

00:04:12.793 --> 00:04:14.962
so these in the Canadian shield.

00:04:14.962 --> 00:04:18.766
Um, so strongly metamorphosed.

00:04:18.766 --> 00:04:21.418
And this tillite is uh, 
weathering very rapidly

00:04:21.418 --> 00:04:23.905
as a result of the intense metamorphism,

00:04:23.905 --> 00:04:26.506
which has caused cracks and fractures

00:04:26.506 --> 00:04:28.776
which increase surface area, of course,

00:04:28.776 --> 00:04:30.927
and cause weathering to accelerate.

00:04:30.927 --> 00:04:35.866
[traffic in background]

00:04:35.866 --> 00:04:37.868
Now realize I'm looking at a shadow here,

00:04:37.868 --> 00:04:43.257
but hopefully you can see 
that the clasts are well-rounded.

00:04:43.257 --> 00:04:48.379
Very poorly sorted, 
in terms of size distribution.

00:04:48.379 --> 00:04:51.013
And are not layered.

00:04:51.128 --> 00:04:53.063
They are unstratified.

00:04:53.063 --> 00:04:56.285
I just thought you might want to see 
what's on the other side of the road.

00:04:56.285 --> 00:04:59.820
That is Lake Superior,

00:04:59.820 --> 00:05:04.141
about an hour south of Wawa, Ontario.

00:05:04.141 --> 00:05:05.660
Pretty big lake, eh?

00:05:05.660 --> 00:05:11.077
Kind of looks like the ocean.

00:05:11.077 --> 00:05:12.948
You can't see the other side 
of Lake Superior,

00:05:12.948 --> 00:05:17.084
even though we're way the heck up 
on the roadside.

00:05:17.084 --> 00:05:23.109
There you can see down to the beach.

00:05:23.109 --> 00:05:24.483
Alright, that's it.

00:05:24.483 --> 00:05:27.429
Bye for now.