Some folds this week from coastal exposures in western Boothbay Harbor, Maine, where I’m on vacation for one more day… Acadian metamorphics (schist, gneiss), with injected granite pegmatite that has also been folded (and boudinaged): Happy Friday!
Okay, I photoshopped that one up. This one too… Here are the originals… And, if you’re a scale-off-to-the-side-of-your-main-subject purist, here’s a different shot of this quintessential boudin: And, while we’re at it, here are some other fine boudins (of granite pegmatite) exposed along the coast of West Boothbay Harbor, Maine: Some nice coastal ecology to … Read more
Pemaquid Point, Maine, is a locally-owned and -managed park near an old lighthouse. I went there yesterday with my family. We’re on vacation in coastal Maine for a week. At Pemaquid Point, the action of waves have cleaned the rocks, and they offer a delightful three-dimensional look at Acadian-aged metamorphics and granite pegmatite dikes, with … Read more
When I was flying back from Phase I of “Border to Beltway” in Texas this past March, I was delighted to photograph a bunch of local geology from the air, including this prominent diabase quarry in Manassas: I had never been to this particular quarry before, but as it turned out, it was one of … Read more
My student James O’Brien took this image of a kink band along the Billy Goat Trail, downstream of Great Falls in Maryland’s metamorphic Piedmont province. A lovely little structure, don’t you think? Thanks, James! Happy Friday, all.
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
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
Todd Redding is our genorous sponsor for this week’s Friday fold. Todd reports that this boulder is derived from the Okanagan Metamorphic Complex near Penticton, British Columbia, Canada. He gives its lat/long as 49°28’14.10″N, 119°30’23.14″W. Did you spot the small fault in there, too? Thanks for sharing, Todd!
Over the summer, I shot these two GigaPans of the “Great Unconformity” in Wind River Canyon (Owl Creek Mountains), Wyoming: link link This week, Team M.A.G.I.C. (by which I mean my student Robin Rohrback-Schiavone) finished up a series of three macro GigaPans of rock samples from the site (made with our one-of-nine-in-the-world GIGAmacro rig by … Read more
Lily and I took our son to the Virginia Scottish Games on Sunday. This is an annual competition of events in traditionally Scottish feats – throwing heavy things, mainly. There is also fried food, whisky, and some terrific music. The event is held at the Great Meadow, south of The Plains, Virginia. I had never … Read more
Using your relative dating prowess to determine which of these two rock units is older, the schist (dark gray) or the granite (light pink): Click to enlarge Click to enlarge Justify your answer by citing a principle of relative dating.
I was up in Carleton College (Northfield, Minnesota) for most of the week, working on a new teaching module for the InTeGrate project. On the way between our work area and the cafeteria where we ate lunch, we passed the geology department’s rock garden. They have some great specimens there, some big, some small. Here … Read more
A week ago, I featured six new GigaPans here, of the extraordinary rocks in Klingle Valley, DC. I hadn’t been able to get the next phase of imaging that site ready in time for the post, but here it is: an annotated view of the outcrop. Annotation color code: PINK = Granite contact BLUE = … Read more
Following on yesterday’s post about the kink bands within the strained metagraywacke of the Laurel Formation in DC, let’s take the opportunity today to go to Klingle Valley, site of a different facies within the Laurel Formation: a strained metaconglomerate. Though the exposure isn’t as great as the Purgatory Conglomerate, I think you’ll find plenty … Read more
Another new insight from last week’s visit to the Outdoor Lab was that they have several fine examples of native copper found in float of the Catoctin Formation on their property. Here are a few examples: Classic examples – a bit of malachite in there too, it looks like. I wasn’t totally shocked when I … Read more
Two years ago, I took a trip to the Phoebe Hall Knipling Outdoor Lab, which is Arlington, Virginia’s outdoor education facility in the Pond Mountains (southern continuation of the Bull Run Mountains), on the eastern edge of the Blue Ridge geologic province. I was invited back last week to look at some new exposures. I … Read more
The Friday before last, I was in DC for a fun geology/botany field trip, and I got the opportunity to stroll around the barn at historic Peirce Mill, a historical grain mill along Rock Creek in Rock Creek Park, Washington, DC. The barn is immediately south of Tilden Street NW. It appears to have been … Read more
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 … Read more
Migmatite is a special rock that is partly metamorphic and partly igneous. Let’s take a look at it in Part 2 of Callan’s “Transitions of the Rock Cycle” series.
An outcrop of the Ordovician-aged Martinsburg Formation is used to illustrate the development of slaty cleavage, and hence a major transition in the Rock Cycle.