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!
[gigapan id=”98833″] GigaPan by Alan Pitts, as part of the M.A.G.I.C. project that we are working on. Here’s another one from a few meters away. Here’s a shot from 2.5 minutes after Alan saw this anticline for the first time. Here’s some shots of my own early visit to the site, after I first found … Read more
Callan and his wife journey to Africa’s southernmost point, and find a geological mystery there.
At the Three Rondavels overlook in the northern Drakensburg Mountains of South Africa, I saw this chunk of quartzite with a peculiar variety of Liesegang banding (iron oxide staining of the rock by groundwater): A short distance away, I found another example: In one key way, I liked this second example better, even though the … Read more
While I was away in South Africa, both Brian Romans of Clastic Detritus and Evelyn Mervine of Georneys posted pictures of folds in quartzite of the Cape Fold Belt in southern South Africa. Well, I’m not going to be left out. Here’s a belated Friday fold for December 23, showing a bunch of sweet folds … Read more
Here’s a piece of vein quartz with a series of interesting “cubist disc” shaped holes in it. I interpret these cavities as external molds of some mineral which has now been physically removed or chemically weathered away. So only its exterior shape remains, and I wonder if that’s enough to identify the mineral that used … Read more
Spotted this one Monday on the newly-rerouted section of the Billy Goat Trail’s Loop A, in Chesapeake and Ohio Canal National Historical Park. This graded bed was deposited as a turbidite in the Iapetus Ocean, sometime in the time-frame of 700 to 460 million years ago. It was metamorphosed 460 Ma during the late Ordovician … Read more
On Monday when I went to Powell’s grave, I noticed a few “boulder with a plaque” gravestones, the most distinctive of which was this lovely chunk of rose quartz: Quartz is a good choice, since it’s very very very stable at Earth surface conditions, and thus will stick around a lot longer than, say, a … Read more
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 … Read more
Today’s Friday fold takes me back 25 years, to when I visited the Outdoor Lab with my science class in Arlington County Public Schools. I revisited this exemplary outdoor education facility on Tuesday, at the invitation of its director, Neil Heinekamp. Neil wanted a geology “expert” to take a look at their rocks, and I … Read more