Callan reviews a book about the historical battle over the meaning of coral reefs. Protagonists include Charles Darwin and the son of Louis Agassiz. The book’s author, David Dobbs, answers some questions for Callan and readers.
While on Callan’s field course in eastern California, student Filip finds a lovely fold sample.
Callan has a conversation with Scott Mandia, a community college professor working on the national level to improve the public’s understanding of climate science.
Callan visits the Sea Point migmatite, a contact between intrusive granite and older metasedimentary rocks, along the west coast of South Africa near Cape Town. His guide? None other than AGU Blogosphere blogger Evelyn Mervine of Georneys!
New M.A.G.I.C. GigaPans are shown of two connected Hawaiian samples: one an igneous rock, one a loose beach sand.
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Callan shows off a new sample from Texas, a peridotite xenolith launched into the air from a maar volcanic eruption, slathered in a layer of basalt. With full intent to coin a neologism, he dubs it a “xenobomb.”
Riding a cable-car up the side of the Franklin Mountains, Callan checks out the local stratigraphy and structure (and igneous intrusions). Join him on an insightful cruise up several thousand feet and through a billion years of geologic time.
Callan looks south across the border from Texas. Above the drug-war-ravaged town of Juarez, the Sierra de Juarez Mountains feature an enormous recumbent synform.
This beastie lives in an old quarry in West Virginia, along old Route 55. And from a slightly different perspective… This fold is in Devonian limestones of the Helderberg Group, kinked up probably during the Alleghanian Orogeny (the assembly of Pangea) in the late Paleozoic.
Callan and his wife journey to Africa’s southernmost point, and find a geological mystery there.
Callan reviews the geology of the superlatively auriferous Witwatersrand Supergroup of South Africa, and then zooms in on a distinctive marker bed near the base of the sequence. The deformation in this particular banded iron formation (BIF) is an aesthetic wonder, as this suite of images reveal. The layer outcrops in the heart of urban Johannesburg.
The Friday fold is found on a newly-opened section of road in West Virginia. Join Callan in checking out some synclines and associated faults in the Devonian-aged Brallier Formation.
Callan and three students visit a world-class outcrop of columnar jointing in Shenandoah National Park.
Callan visits a new outcrop of highly-sheared rocks in the basement complex of Virginia’s Blue Ridge province.
The “Friday fold” is an isoclinal dextrally-asymmetric granitoid vein exposed north of Fort Frances, Ontario. Taken on October 7, 2011, the photo features a centimeter-demarcated pencil for scale. It shows thickened hinges, boudinage of the lower right long limb, and incipient boudinage of the upper left long limb.
The Friday fold is a guest photo by James Edward Bailey, a 5th grade student from Reston, Virginia. It is the anticline shown is known as “the Devil’s Backbone,” located near Marlinton, West Virginia, right on the boundary between the Valley & Ridge province and the Appalachian Plateaus. It clearly shows differential weathering of weaker layers and tougher layers. …Also some lovely fall colors!
Northern Colorado’s route 287 connects Fort Collins, Colorado with Laramie, Wyoming. Along its length, it displays roadcuts into Archean-aged basement complex. Two of these outcrops are featured in this post: one metamorphic (mostly), and a second igneous (mostly), with some intriguing polka-dotted plutons.
“Clinker” is an interesting rock type seen in Wyoming’s Powder River Basin. It forms when a coal seam catches fire, and cooks the rock above and below it, including the potential for partially melting the strata immediately above. Check out a few images of this intriguing rock here.
A up-to-date tally of the aftershocks from the Mineral, Virginia earthquake is presented as a time vs. magnitude plot.
The Friday fold is a gorgeously deformed “duplex structure” in Mesozoic limestones of southwestern Montana.