Callan Bentley We have a guest Friday fold today, from reader Ben Mackay-Scollay of the Monash University School of Geosciences in Melbourne: Ben writes: Hey there Professor Bentley, been a fan of your blog for a while and I thought you might be able to use this for your Friday Fold series. It’s an upright fold at … Read more
These four slabs, collected at “Fossil Hill,” north of the Cristo Rey laccolith at the Chihuahua (Mexico) / Texas / New Mexico triple point, bear positively-weathering fossils of the benthic foraminiferid called Cribratina, an index fossil for the Albian age / stage: My field notebook serves as an imperfect sense of scale. Here’s the Albian … Read more
On “Border to Beltway”‘s visit to Kilbourne Hole, after we whet our appetite with Hunt’s Hole, Michael finds a xenobomb. Ernie and Boris look on with envy: A “xenobomb” is a xenolith (in this case, of mantle peridotite), slathered in a coating of lava and tossed out of a volcano in the middle of a … Read more
On Saturday of this past weekend, I led a field trip to Sideling Hill and Paw Paw Tunnel, and on the (1.5+.75+1.5=) 3.75 total hours of driving, I listened to the audio book version of Tim Cahill’s short book on traveling around in Yellowstone National Park. It’s a fun little book, but I wished it … Read more
Check out the immense climbing ripples preserved in surge deposits at Hunt’s Hole (a maar volcanic crater in southern New Mexico) and imagine the strong currents couples with an extraordinary amount of entrained pyroclastic material.
It’s Friday… that means it’s time for a fold. Let’s try this outcrop at “Confusion Hill” in the Franklin Mountains of West Texas: See it? Let’s zoom in… From the shadows to the left of the hammer, trace out the dark green layer… it may make you think of a box fold: …but it’s not. … Read more
That’s Aden Crater, a Pleistocene shield volcano in southern New Mexico. Here’s what it looks like from above (Google Maps view): I also noted the position of two nearby maar craters: Kilbourne and Hunt Holes. When you climb up to the edge of Aden and look in, you see the congealed and fractured remnants of … Read more
Good morning! Let’s take a walk up the east side of the Franklin Mountains, north of El Paso, Texas, to walk across the Great Unconformity. The basement rock exposed here is the Red Bluff Granite, a 1.1 Ga felsic magma that intruded the columnar basalts of the Mundy “Breccia” and the Castner Marble. (It is … Read more
While I’m showing photos from last week’s Billy Goat Trail field trips (3 in total), let me share a striking example of root wedging from Olmstead Island, on the walkway out to see Great Falls: And, since I meant to get back to blogging about west Texas this week, here’s another example of the same … Read more
Here’s a sweet little sample of migmatite (~470 Ma late Ordovician Taconian Orogeny, U/Pb date from zircon), that my students and I spotted last week on the Billy Goat Trail, downstream of Great Falls in Maryland’s metamorphic Piedmont province: Note the white translucent quartz, the orangey (partially kaolinitized and rusty stained) opaque potassium feldspar, and … Read more
I know nothing about this sample, other than the fact that it was a thrown-away sample found in the rock pile next to the old geology building at the University of Texas at El Paso. Happy Friday!
Today, I initiate a series of posts based on some of the geology I saw over spring break, in west Texas and southern New Mexico, on the field exchange between Northern Virginia Community College and El Paso Community College that I helped facilitate. We spent our first morning in the field in the Franklin Mountains, … Read more
A young-Earth creationist reinterprets one of Callan’s blog posts in light of a Biblical flood. Callan responds with a demonstration of how new information can change a true scientist’s mind, but no amount of data can convince someone whose conclusions are based on faith rather than empirical data.
Where the Needmore Formation is falling apart on Corridor H, sloughed-off shale is piling up in a tiny talus slope: You could slap a protractor on that photo and get a pretty good measurement of the angle of repose of this chippy, flaky granular material. Eyeballing it, that looks like about 45° to me.
Howard Allen returns with a Friday fold contribution for this week. He says: Not exactly a fold, but I thought you’d like this rolled boudin(?) (quartz) in a muscovite garnet schist (note garnets above the lens cap). This specimen is also from the Shuswap Metamorphic Complex, north of Sicamous, British Columbia. Lovely. Thanks for sharing, … Read more
I just wanted to let readers know that posting will be light this week, as I’m down in Texas running my field exchange course with Joshua Villalobos of El Paso Community College. Joshua’s supplying 12 students, and so am I. Together with talented colleagues, we’re aiming to give these students, many of whom hail from … Read more
Happy Friday! Here’s a beautiful folded obsidian sample, replete with conchoidal fractures, on display outside the geology department at Arizona State University in Tempe, where I was last week:
The Wallbridge Unconformity is a surface of stratigraphic hiatus or erosion between the depositional influence of the Tippecanoe and Kaskaskia epeiric seas. After Alan Pitts and I located ourselves in the Oriskany Sandstone (terminal Tippecanoe stratum), we looked stratigraphically above the quartz sandstone for the overlying unit, which should be the Needmore Formation shale (beginning … Read more
Today, a few more photos from the field trip last month to Corridor H, the fine new superhighway with so little traffic out in eastern West Virginia. Our antepenultimate stop of the day was at an outcrop we inferred should hold the Oriskany Sandstone, a Devonian quartz arenite that lies stratigraphically above the Helderberg Group … Read more
I recently read God’s Harvard, by Washington Post reporter Hanna Rosin. It’s a profile of the people and philosophy behind Patrick Henry College, a private Christian college located not too far from me, in Purcellville, Virginia. PHC is an Evangelical place that strives to serve its homeschooled matriculating freshmen with a sense of worldliness and … Read more