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30 November 2022
Another glimpse of sand on the beach at Esterillos Oeste, Costa Rica… This time, I offer you a trace of an organism moving through the wet sediment: Note the two parallel lines of tracks laid down by little feet, and the central groove that overprints them. It reminded me very much of this similar arrangement, from near St. Andrews in Scotland, but: (1) this is the underside of a bed …
30 December 2021
Callan reviews Scottish author David Farrier’s nonfiction exploration of humanity’s signatures on the geologic record.
29 January 2021
I have two Friday folds for you today, both by geovisualizers who contributed to the 2019 Geological Society of America Pardee Symposium on Geoscience Communication in Phoenix, Arizona: The first is a painting by talented geoartist Emma Theresa Jude, showing a fold at Caithness, Scotland. The fold in question can be seen at the site of Figure 5 of this paper. I love Emma’s art. What other lovely folds have you …
20 January 2020
A quartet of brief book reviews from some of Callan’s recent reading.
20 May 2019
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
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
What can we learn from Scotland’s Parallel Roads of Glen Roy?
22 August 2018
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
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 showcase of five new 3D digital models of awesome rock samples and outcrops, produced using Agisoft Photoscan.
3 May 2017
The answer to yesterday’s geo-puzzle is revealed to be a storm deposit of boulders, 20 m above sea level!
12 April 2017
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
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
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.
3 March 2017
Let’s reminisce back to the Walls Boundary Fault on the Ollaberry Peninsula of Shetland today. Here’s a 3D model to go along with the ones I posted last time: It’s a little ragged, but so am I at the end of the workweek! Happy Friday. Have fun spinning this thing.
2 March 2017
On the northwestern coast of the Northmavine Peninsula of Shetland, there is an unusual coastal landform: a gate-like entrance to an elevated amphitheater, like something out of Tolkien, and a storm beach of slab-like boulders inland of that.
1 February 2017
In eastern Shetland, the sea chews away at the innards of a Devonian stratovolcano. But there’s an odd visitor there too – and we’re not talking about the blogger.
26 January 2017
The scenic arch of Dore Holm (“Door Island”) in Shetland shows off the most efficient way of breaking a slab of rock. The island’s shape is a reflection of the parsimonious nature of natural deformation.
16 January 2017
A quest to visit the “first shear zones” described in the scientific literature leads to an alternate location, and some GIGAmacro images of samples from the real, original spot.
13 January 2017
On the western coast of Islay, Saligo Bay showcases turbidites of the Neoproterozoic Colonsay Group. The Smaull Graywacke shows Caledonian (late Ordovician) folding and cleavage superimposed on world-class graded bedding. There’s also a nice dolerite dike to examine.