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5 December 2022
Got these photos from a reader, showing outcrops in the northern Wind River range (ESE of Island Lake). The question, inevitably, is are these MMEs (microgranular mafic enclaves) or xenoliths? They’re fine grained and mafic… but some lithologies of xenolith could be too! This next set shows what appear to be a bunch of blocks strung out in a line… This one is shaped like a toaster or a television …
25 June 2021
Inside the Blue Ridge (in an 1850s-era railroad tunnel), Callan finds folds and boudinage that formed during Appalachian mountain-building.
7 May 2021
On his way to get his COVID vaccine, Callan visits a new outcrop showing folded and faulted strata of the Neoproterozoic Lynchburg Group.
9 August 2019
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.
11 July 2019
Traveling in Newfoundland, Callan visits a seaside outcrop showing a Proterozoic submarine slump complex, overprinted by tectonic cleavage and weathered by the sea.
22 March 2019
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!
5 June 2018
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.
8 February 2018
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!
2 February 2018
The Friday fold is a really cool 3D model of differentially-weathered calc-silicate rocks in Scotland that were folded during the Caledonian Orogeny.
2 November 2017
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 …