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25 June 2021

Friday fold: The Blue Ridge Tunnel

Inside the Blue Ridge (in an 1850s-era railroad tunnel), Callan finds folds and boudinage that formed during Appalachian mountain-building.

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7 May 2021

Friday fold: Lynchburg Group

On his way to get his COVID vaccine, Callan visits a new outcrop showing folded and faulted strata of the Neoproterozoic Lynchburg Group.

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9 August 2019

Friday fold: crumpled green metavolcanics from St. Anthony

The Friday fold erupted out of a volcano, completing the second part of its two stage cooling history, then later got folded and metamorphosed. It was found atop a high cliff near the northern Newfoundland town of St. Anthony.

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11 July 2019

A submarine slump complex at Sandy Cove, Newfoundland

Traveling in Newfoundland, Callan visits a seaside outcrop showing a Proterozoic submarine slump complex, overprinted by tectonic cleavage and weathered by the sea.

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22 March 2019

Friday fauxld: concentric weathering rinds

Here’s a deceptive Friday “faux”ld I saw last week on the South Page Valley Road whilst learning about the Martinsburg Formation outcrops there: Looks like an isoclinal fold in this slab of siltstone, but the curvy lines are just concentric weathering rinds. Not a real fold at all! I hope everything you see this weekend is more straightforward and less deceiving. Happy Friday!

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5 June 2018

Cross-bedding in Archean komatiitic ash deposits

Cross-bedding isn’t just for modern sedimentary deposits; you can find it in truly ancient ash deposits too! Let’s head to South Africa and take a look.

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8 February 2018

A spectacular display of Earth science in the Alabama Hills

A detailed examination of an elegant photo of the eastern front of California’s Sierra Nevada, from the perspective of the Alabama Hills. How many different geologic phenomena can be packed into a single image? Let’s find out!

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2 February 2018

Friday fold: 3D model from the Portsoy Shear Zone

The Friday fold is a really cool 3D model of differentially-weathered calc-silicate rocks in Scotland that were folded during the Caledonian Orogeny.

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15 January 2018

Monday Geology Picture: Constantia Granite

For this week’s post, here’s a picture that I took yesterday during a Sunday afternoon hike with my family. We went for an easy stroll, baby and all, along the Alphen Trail in the Constantia region of Cape Town here in South Africa. My son is 3 months old now, and we’re just starting to go on some easy hikes as a family. The Alphen Trail is more of a …

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2 November 2017

Weathering in komatiite

This morning on Twitter I was reminded of komatiites, those “extinct” ultramafic lavas that were relatively common eruptions during the Archean. I’ve actually got a good number of komatiite photos to share from my time last year in South Africa’s Barberton Greenstone Belt. But since time is short this morning, I’ll start with a short photo set of three images, all showing different aspects of how these ultramafic rocks weather …

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18 August 2017

Friday folds: the Roman Forum

When in Rome, do Friday folds as the Romans do? Here are some images from my brief, sweltering visit to the Roman Forum(s) this past summer. The whole region is a jumblepile of ancient ruins in a thousand styles. Almost nothing is labeled. It looks like this: This particular building held up a bit better, and its lovely columns sported some folded marbles: Close-up shots to show the folding internal …

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5 June 2017

3D models of sedimentary structures

I’ve been busy making 3D models lately. Here are three ones united by a theme of being sand that was deposited relative to mud. In one case we have scouring to make flutes, in another case we have have localized sagging to make “ball & pillow” structures, and in the third case we have an extraordinary submarine landslide deposit. For two of them, the shale has been preferentially etched away, …

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17 April 2017

Liesegang rings in a natural sandstone “tile”

An easter egg on a piece of toast? No, it’s a nice example of Liesegang rings in a slab of sandstone. Explore more in this blog post.

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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 …

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28 March 2017

P-sol in a conglomerate countertop slab

A hardware parking lot in rural Virginia showcases an elegant slab of pressure-solution induced compaction of a conglomerate.

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13 February 2017

Q&A, episode 2

A new edition of “science and nature question and answer.” This week: why Massanutten Mountain isn’t longer, and why you’re never going to walk on the Sun.

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13 January 2017

Friday fold: Smaull Graywacke at Saligo Bay, Islay

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.

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8 December 2016

Silent samples, holey samples

Two very different samples tell stories that are full of holes. What’s going on with this weathered sandstone? What’s going on with this fossil scallop shell?

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30 November 2016

“Drumsticks” of Islay tillite

One fun thing about examining the Port Askaig Tillite in the field is to find odd-shaped exemplars of the unit lying on Islay’s beaches. My favorites were shaped like wands, or antennae, or perhaps the drumsticks freshly detached from a Thanksgiving turkey… a big clast at one end and then a thin septum of the finer-grained matrix to hang on to: Here’s an example: The shape results from differential weathering …

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3 October 2016

A virtual field trip to Rathlin Island, Northern Ireland

Rathlin Island lies north of mainland Northern Ireland, a few miles offshore. I spent three lovely days there this past summer, investigating the geology and appreciating the wildlife (puffins and other sea birds, and seals). The geology is pretty straightforward: Paleogene basalt overlying Cretaceous “chalk” (really not so chalky here – technically, it’s the Ulster White Limestone). Here’s a suite of interactive imagery that you can use to explore Rathlin’s …

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