Page 32 - A Geology Walk up the Clyburn Valley

ISSUE : Issue 67

Published by Ronald Caplan on 1994/8/1

;';;'._ A view of one of the boulder bars in Clyburn Brook; see text, bottom of page 33. can see it clearly from the trail itself, in silhouette there against the clouds. When you see something like that (chim? ney) , you know you're dealing with land? slides. Erosion doesn't produce a chimney very readily. Erosion will produce a pil? lar around a coastline. But when you see a pillar up on the hilltop there, you know that you're dealing with a landslide. (We walk on.) The road is level in front of us, and this bluff on our right is full of boulders and sand. The material that it's made of is called till. In Britain they call that boulder clay. I think that's a better description of it because that's what it is, is boulders and clay mixed together. And it's material that was deposited when the glaciers melted back at the end of the Ice Age. They were carrying an enormous amount of debris, boulders, and fine-grain material that had been pul? verized inside the glacier or on the base of the glacier--ground up into clay--al? most like rock flour. And that material all got deposited here. Now here it's quite sandy as well because there's a granite nearby. And granites tend to have grains inside them that are CATERING TO ALL YOUR HEALTH FOOD NEEDS about the size of sand grains. And so it's a little bit sandier than most of them. But it's a very unsorted, jumbled mess of some big boulders--not huge but big enough--and the sandy material. Maybe we'll see some landslides further up--I'm not sure. But if you poke around in it, sometimes you'll find that there actually is layering in it. It's not as jumbled as it at first looks. What we see here is the stuff falling off the side of the face and just falling down onto the road. The whole riverbed is filled with glacial detritus. Glacial material that got dumped by the ice as it moved down the valley. Some of it got dumped as the ice melted away. Some of it was being dumped as the ice was moving down, before the ice melted away. (Driven before it?) Or just piled up underneath it. Now, I'm not sure how deep the valley ac? tually is here. I would expect that it's probably another 50 to 100 metres deeper than where we're standing. I'm sure the river valley, the bedrock at the bottom of all these boulders and sand and clay--the bedrock is below sea level. But that's typical of any of these deep mountain valleys that have been carved out by glaciers. • Herbal Remedies & Teas • Vegetarian Foods • Free Range Chiclcens & Eggs • Nut Butters • Dairy Free Ice Cream & Cheese • Tofu • Body Care Products • Juices & Grinders • De-Alcoholized Wines & Beer • Buli( Foods tSti??cLa&2Lnq in 'W'ai 't • ? & U'aiztf 'i • ? 0oJucii J2CLJ2CL 1 natuxaL fooai 156 FALMOUTH ST., SYDNEY CiC' 'Ad (NEAR CENTRE 200) 'DX" / UO%J But what we see here is this river has actually filled in its valley. Filled in with unsorted boulders and sand. You wondered whether this was actually deposited by the ice or deposited by the river and cut down through by the river. I think it's probably a bit of all. Some of it was dumped by the ice sheets. Some of it was dumped by riv? ers which drained off the ice sheet. And some of it was cut through by the river as well. You can look up the river, and you can see how it winds back and forth from

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