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30 July 2022

Well-preserved mudcracks in Belt argillite, Glacier National Park, Montana

Fresh from the field, Callan shares a quintet of beautifully preserved desiccation cracks in Mesoproterozoic Belt Supergroups sediments, exposed in Montana’s geological gem, Glacier National Park.


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24 December 2016

A wondrous transformation

It’s bonfire season here in the Fort Valley. I live in a forest, and that forest is full of dead and downed wood. Motivated by a desire to (a) reduce forest fire risk and (b) clear out some of the area under the trees for unobstructed recreation, I gather it up and periodically burn it off in batches. We time these blazes to the weather – before or after after …


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19 August 2015

Iron oxide sweat stains in sandstone

What do a sweaty baseball cap and fractured sandstone have in common? Episodes of absorption of dirty liquids that pile up material such as iron oxide at the soaking front.


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20 May 2015

Liesegang banding in Pennsylvanian sandstones, Bolt Mountain, West Virginia

While out at the eastern section of NAGT’s annual meeting last weekend in West Virginia, I participated in a field trip to look at the stratigraphy of the Bolt Mountain section of Pottsville Group strata. One thing that was particularly eye-catching about the sandstones we saw was that many of them had been stained by rusty groundwater, producing the lovely stripey pattern known as Liesegang banding. Here are five examples: …


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4 November 2014

Joints highlighted with hematite, Anapra Sandstone, Cristo Rey

Good morning. Here are two images from last March’s “Border to Beltway” field trip to West Texas, on the north flanks of the Cristo Rey laccolith. Specifically, these are Cretaceous strata of the Anapra Sandstone, looking at the bedding plane of the rocks. Cutting across bedding are a series of fractures (joints) that have been highlighted by the oxidation of iron (rusting) along their edges. In the first photo, the …


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1 September 2014

Field work on the Grinnell Formation at Red Rock Canyon, Waterton Lakes National Park, Alberta

Callan’s Rockies field course students document faulting and jointing in Red Rock Canyon, Waterton Lakes National Park, Alberta.


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17 April 2014


I found this interesting looking slab of gray limestone last summer in the Bridger Range of Montana, in one of the talus slopes on the north side of Sacagawea Cirque. The high-contrast pattern reminded me of something, but I couldn’t say quite what. Then I realized: it looks like one of those indigenous pictographs, where the artist puts their hand up to the rock and spits paint all over it, …


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6 February 2013

Dinosaur footprints in west Texas

Everything’s bigger in Texas, even the footprints…


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9 January 2013

Hoerikwaggo Trail 3: Joints, veins, and Liesegang banding

Callan continues his week-long recounting of his five-day backpacking trip from the Cape of Good Hope to Cape Town, South Africa, along the Hoerikwaggo Trail. Today, we examine the jointing, oxidizing and reducing fluid flow, and the emplacement of ore veins.


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2 February 2012

Beautiful rust

Rust swirls on shale fragment, new New Route 55, Valley & Ridge province of West Virginia. I’m not sure if I can call this “Liesegang banding,” since it’s just on the joint surface (two-dimensional) rather than permeating the rock in a three-dimensional blob. Anyhow… It’s pretty.


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