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11 October 2016
A virtual field trip to Portrush, Northern Ireland
One of my favorite places in Northern Ireland is the east side of the peninsula that hosts the tourist town of Portrush. There, two early schools of geological thought engaged in a battle. The opposing sides were: the Neptunists, who thought all stratified rocks, and in particular basalt, must form from precipitation from the sea, and the Plutonists, who thought some rocks, including basalt, formed through intrusion of molten rock …
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: Diorite from the eastern Sierra Nevada of California: Vein cross-cutting foliated & lineated gneiss, Blue Ridge basement complex, Virginia:
19 December 2014
Friday Fold: Mist Mountain Formation in Canmore, Alberta
Let’s journey to the Cretaceous today, to see sandstones, shales, and even some coal strata that have been folded during the eastward thrusting that built the Canadian Rockies. Here’s the same fold, in context, shot in GigaPan on a different day, from a different angle. Can you match it up? link Ben Gadd showed me (and my field class) this site last summer. It’s a little west of Canmore. There’s …
12 March 2013
Five new GigaPans from Thoroughfare Gap
Yesterday, I took five new GigaPans at Thoroughfare Gap, a water gap where Broad Run cuts through Bull Run Mountain, the eastern limb of the Blue Ridge Anticlinorium at my latitude. The rocks here are the Cambrian-aged Chilhowee Group, with bedding tilted moderately to the east during Alleghanian mountain-building in the late Paleozoic. To the west is the crystalline core of this massive regional fold, and to the east is …
15 November 2012
Neoacadian Inner Piedmont trip, part III: Mesozoic cataclasite
Quartzite, shattered and healed and shattered again and again and again. It’s cataclasite, seen in the North Carolina Piedmont and inferred to be Mesozoic in age due to its brittle style of deformation.
19 October 2011
Bookshelfed mullions from Norway
Elizabeth Eide of the National Academies shared this image with me a year or two ago, when she gave a talk on Norwegian geology for the Geological Society of Washington. Those are some bookshelfed gneiss layers sandwiched between upper-left and lower-right carbonates. The “bookshelfing” refers to the numerous parallel brittle fractures along which the gneiss slabs have slid down the face of their neighbors, like a set of encyclopedias tilted …
25 March 2011
Friday fold: conference samples
At last weekend’s northeastern / north-central GSA meeting in Pittsburgh, David Saja of the Cleveland Museum of Natural History presented a talk entitled, “Geometric Analysis of Folded Greywacke Layers from Pacheco Pass, California.” [Abstract link] In addition to the standard PowerPoint presentation that 99% of GSA speakers use, David also brought in some hand-samples (what we in the business like to call pocket folds) to display. As his title implies, …
24 December 2010
GoSF6: Graywacke turbidites
The geological tour of San Francisco continues with an examination of the graywacke deposits of the
21 December 2010
GoSF3: Chert
Episode three in the multi-part series on the geology of San Francisco. This post focuses on the chert layers of the Marin Headlands
20 December 2010
GoSF2: Basalt
Second in the on-going series about the geology of San Francisco: this post explores the pillow basalts of the Marin Headlands Terrane.
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.