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20 May 2019
Digital manipulation as a teaching aid
Photoshop is a powerful image editing program. Its “cloning” tool allows the removal of “distracting” data from geological imagery. Examine these four examples and consider the ethical limits of the technique. Is it okay to remove fractures and lichens from an outcrop photo in order to allow novices to focus on the geological content you want them to learn from?
6 February 2019
Dalradian schist at Glen Roy
We saw last week how glaciation carved out a valley in Scotland called Glen Roy. As the glacier ground into the landscape, it liberated tremendous numbers of sedimentary particles from the bedrock, which is composed of Dalradian metamorphic rocks (mainly porphyroblastic schist in my observation). Then once that now-U-shaped valley had been deglaciated, a new glacier dammed it, making a lake that rose and filled the declivity of Glen Roy, …
29 January 2019
The Parallel Roads of Glen Roy
What can we learn from Scotland’s Parallel Roads of Glen Roy?
22 August 2018
Q&A, episode 5
A reader asks: “What is foliation and what makes it so important to the structure of rock?”
Callan answers with a lot of images of beautifully foliated rocks.
1 March 2018
A GIGAmacro view of a cool outcrop in Scotland
As noted previously, the old way of viewing gigapixel imagery is no more. But there is a new, better way. The GIGAmacro company has a better viewing platform that can be used either with images uploaded to their server or with pre-existing images that currently “live” at GigaPan.com. Here’s an example: a roadcut of limestone of the Grudaidh Formation (Durness Group) in the Northwest Highlands of Scotland, near Ardvreck Castle, …
9 August 2017
A suite of new 3D models
A showcase of five new 3D digital models of awesome rock samples and outcrops, produced using Agisoft Photoscan.
3 May 2017
Storm beaches have I loved
The answer to yesterday’s geo-puzzle is revealed to be a storm deposit of boulders, 20 m above sea level!
12 April 2017
Weathering along perpendicular joint sets, Arran
Check this out: That’s a beautiful example of weathering in a dolerite dike on Arran. The igneous rock was broken along two more or less perpendicular joint sets, and then fluid flow along those fractures helped “rot” the adjacent rock through oxidation and hydrolysis. The resulting brownish weathering rind grows at the expense of the unweathered black rock. Because there is more surface area at the corners of the rock …
6 April 2017
Stac Fada
The evidence for a meteorite impact origin for the Stoer Group’s Stac Fada member seems to stack up. Engage in a virtual field investigation on Mountain Beltway.
9 March 2017
Lugworm casts on the beach, Islay
Who dwells beneath the sands of Islay? Lugworms do. These embedded annelids process the sediment for food, extruding the undigested sand in charismatic piles that adorn the beach of Loch Gruinart.
Callan Bentley is an assistant professor of geology at Northern Virginia Community College. He is a fellow of the Geological Society of America and the 2018 National Association of Geoscience Teachers' James Shea Awardee. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. Callan served as a contributing editor at EARTH magazine for many years. He is Past President of the Geological Society of Washington and the Geo2YC division of NAGT. He lives in the Fort Valley of Virginia.