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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.


22 May 2020

Friday fold: Anticline in Glacier National Park

Some web research led to a serendipitous discovery and further exploration. Wherever you’re sheltering in place, you don’t have a view that’s this grand. Slip away for a few moments to the high country of Montana’s Glacier National Park, where an anticline may be seen in the towering cliffs…


2 August 2019

Friday fold: kinks in gritty phyllite near Lawn, Newfoundland

The ‘Friday fold’ shows gorgeous conjugate sets of kink bands transecting the plane of foliation in some phyllitic metasediments seen on the southern Burin Peninsula of Newfoundland.


27 July 2018

Friday fold: new folds from the Empire Formation, Glacier National Park

Hiking Siyeh Pass in Glacier in Glacier National Park on Tuesday with my Montana State University field course, we spotted a few new folds in the Empire Formation (a transitional unit between Helena Formation and Grinnell Formation). Here is one of the students serving as a sense of scale, with interesting features on either side of him: On the left, there are small scale folds in a regular little train: …


28 July 2017

Friday fold: Big kink fold in Grinnell Formation

It’s Friday! How about we celebrate with a beautiful kink fold from a gorgeous national park?


15 April 2017

Basement xenoliths in Catoctin Formation, Compton Pass

My son and I hiked Compton Peak in Shenandoah National Park this morning, and saw these two lovely examples of xenoliths. The example above is small, but it shows clearly the difference between the coarse, felsic basement rock (Mesoproterozoic granitoid, comprising the xenolith) and the surrounding fine-grained dark green metabasalt of the Catoctin Formation (Neoproterozoic). Here’s another, bigger example: These two Blue Ridge examples both illustrate the principle of relative …


29 October 2016

New digital media of Shenandoah National Park feeder dikes

In Shenandoah National Park, astride Virginia’s Blue Ridge, feeder dikes of Catoctin Formation (meta-)basalt cut across the Grenvillian-aged granitoid basement. Due to their mafic composition and columnar jointing, these feeder dikes generally weather more rapidly than their host rocks. I led a field trip in the park on Thursday for my son’s school, and my student Marissa was there the weekend prior, checking out the autumn leaves and geology with …


16 September 2016

Friday fold: Centenary migmatite

The Friday fold is a guest submission from Bill Burton, who took the photo of these lovely ptygmatic folds in migmatite in a national park on the 100th anniversary of the founding of the Park Service.


27 March 2016

Another trio of 3D models

Here are three more of my Photoscan-generated, Sketchfab-hosted 3D models of rock samples: Mud cracks in Tonoloway Formation tidal flat carbonates, Corridor H, West Virginia: [sketchfab id=”49cfc017248e44c2aa8b8bcdfa18facd” start=”0″ spin=”” controls=”0″] Diorite from the eastern Sierra Nevada of California: [sketchfab id=”36184956acb94476ae84569b8fbc300b” start=”0″ spin=”” controls=”0″] Vein cross-cutting foliated & lineated gneiss, Blue Ridge basement complex, Virginia: [sketchfab id=”1ebf2edc042d4cdf9493d0ff7963aff5″ start=”0″ spin=”” controls=”0″]