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27 June 2011
Goose Egg / Tensleep contact
West of Shell, Wyoming, on route 14, there is a lovely exposure showing the tilted stratigraphic contact between the lower Tensleep Formation (purple; Pennsylvanian period) underneath Goose Egg Formation (orange/tan; Permian to Triassic in age). The contact dips to the west because it has been deformed during Laramide mountain-building (uplift of the Bighorn block, and downdropping of the Bighorn basin). Here’s a gigapan to show the contact:
2 June 2011
Conglomerate from Dolly Sods
While my focus was more on bugs and plants than geology this time around, I did hike a new trail at Dolly Sods this past weekend, and on that trail I found several nice boulders of conglomerate. These stood out as being much coarser than the pervasive quartz sandstone of the Pennsylvanian-aged Conemaugh Group which otherwise dominates the outcrops and float of Dolly Sods. Therefore, they were photo-worthy. The conglomerate …
25 April 2011
Two joints
Stopped at Sideling Hill, Maryland, a few weeks back with my three Honors students, on our way to Pittsburgh for the northeast/north-central GSA section meeting. Robin took this photo of me with some sandstone beds that reveal two nice examples of joint anatomy, complementary in their structure: First focus in on the area right of where my finger is pointing. It shows well-expressed plumose structure, little lines that point in …
18 February 2011
Friday fold: Jefferson River Canyon
Here’s your Friday fold, straight from the canyon of the Jefferson River, near Cardwell, Montana. Perspective is to the south. East is on the left; west is on the right. Bigger version This is right next to the outcrops of LaHood Conglomerate that I mentioned earlier this week. My Rockies course co-instructor Pete Berquist and I bring the students here for several reasons, including the conglomerate, nearby Lewis & Clark …
7 September 2010
Dolly Sods
Over the long Labor Day weekend, my fiancée Lily and my friend Seth and I took a three-day backpacking trip in the Dolly Sods Wilderness area of West Virginia: Dolly Sods is a unique place, a little patch of flora that is more typical of Canada. It sits atop the eastern Continental Divide, and most of the area drains to the Gulf of Mexico via the Ohio River. Parts of …
30 March 2010
Sugarloaf
Sunday morning, NOVA adjunct geology instructor Chris Khourey and I went out to Sugarloaf Mountain, near Comus, Maryland, to poke around and assess the geology. Sugarloaf is so named because it’s “held up” by erosion-resistant quartzite. It’s often dubbed “the only mountain in the Piedmont,” which refers to the Piedmont physiographic province. Here’s a map, made with GeoMapApp and annotated by me, showing the general area: A larger version of …
26 March 2010
Transect debrief 6: folding and faulting
Okay; we are nearing the end of our Transect saga. During the late Paleozoic, mountain building began anew, and deformed all the rocks we’ve mentioned so far. This final phase of Appalachian mountain-building is the Alleghanian Orogeny. It was caused by the collision of ancestral North America with the leading edge of Gondwana. At the latitude of Virginia, that means northwestern Africa (Morocco and/or Mauritania). Whereas the first two pulses …
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.