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19 April 2019

Friday fold: Angel Island “III”

For the third Friday in a row, “Mountain Beltway” features folds from Angel Island, in northern San Francisco Bay, California, This time, it’s meta-cherts on Perles Beach, showing impressive metamorphic recrystallization reactions.


25 April 2018

Natural Bridge State Resort Park, Kentucky

A visit to a natural sandstone arch (or “bridge” as the locals call it) in eastern Kentucky yields unexpected bonuses, like fossil wood, Liesegang banding, and the honeycomb-like weathering pattern called “tafoni.”


30 June 2016

Virtual field trip to Siccar Point, Scotland

Time for another virtual field trip on the Geologist’s Grand Tour of the United Kingdom: the most famous outcrop in the world. Today, we visit Siccar Point, Scotland. You’ve probably already seen photos of this place – they usually look something like this: To those who aren’t familiar, here’s what going on: There are two sets of strata here – and the contact between them is an ancient erosional surface. …


24 March 2016

Three new 3D rock sample models

Pahoehoe “ropes” on a basalt, sample site unknown: [sketchfab id=”d846c69192804bcfbcb2a625fd807af1″ start=”0″ spin=”” controls=”0″] Archean gneiss from the Gallatin Range of Montana: [sketchfab id=”4abba639632945aa8bd93c0d4e996e6a” start=”0″ spin=”” controls=”0″] Tafoni in Malmesbury Group turbidites, South Africa: [sketchfab id=”ddb2ec0a22214192907886d56e17ad11″ start=”0″ spin=”” controls=”0″]


20 September 2011

Giant City State Park, Illinois

Giant City State Park is a patch of protected forest south of Carbondale, Illinois, where there are some pretty cool exposures of Pennsylvanian-aged Makanda Sandstone. Here’s a typical look at one: Notice the deep chasm on the right. This leads, maze-like, to other flat-bottomed and vertically-walled canyons: The orthogonal joint sets produces some nice tall, cliff-like vertical exposures that reveal the history of these rocks in several stages: deposition by …