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15 September 2023

Friday fold: Candler Formation

On a birding hike yesterday morning, I found this: This is a little slab of kinked phyllite of the Candler Formation. This metamorphic rock started as mud (and ash) deposited atop the Catoctin Formation, and it was later squeezed and heated during Appalachian mountain-building, encouraging the growth of micas at the expense of clay. A strong differential stress made sure those micas grew in one preferred orientation, and that resulted …


28 July 2023

Friday fold/fauxld duet from Glacier National Park

When is an apparent anticline not an fold? Find out on this week’s edition of the Friday Fold…


14 July 2023

Friday fauxld: Sacagawea Cirque

Found this beautiful cobble while hiking Sacagawea Peak with my family yesterday, in Montana’s Bridger Range. It’s not actually folded as much as it appears to be; the laminations are slab like and nearly parallel to the surface in this photo, with the cobble surface sectioning them obliquely to produce this pattern.