Sunday, December 28, 2014

Year-end accounting

Hello, everyone, at the end of 2014 and the beginning of 2015. There isn't a whole lot going on, so I thought I'd check in on a couple of things. First of all, how did Equatorial Minnesota do this year? To the surprise of absolutely no one, the most-read articles were those involving dinosaurs. The champion was "A brief history of dinosaurs on the Internet". Quite astonishingly, the second favorite was... "Fossils of the St. Peter Sandstone". This is not a knock on its quality, or the subject matter, or... well, I suppose it is, after all. The only explanation I can think of is that it is linked somewhere I can't find, perhaps on a forum or class website. A few personal favorites:
"Platteville Follies: a crushed giant rodent from Hidden Falls"
"Where to see metro geology, part 5: Shadow Falls Park"
"Sponge detective: when faunal lists go bad"
"Designasaurus II"
"Thescelosaurus: hello old friend"

Sunday, December 21, 2014

The Glenwood Formation

Beneath the Twin Cities, sandwiched snugly between the crumbling off-white edifice of the St. Peter Sandstone and the proudly jutting gray to tan Platteville Formation, is a gray to brown layer about 3 to 5 feet thick (or about a meter to a meter and a half for our metric friends), composed primarily of shale. This is the Glenwood Formation, sometimes known as the Glenwood Shale (which is a bit of misnomer because of the sand content). Like a fawn or baby bird, it hides from the eye, although we know it must be there, because heavens knows where else we would get adult deer and birds, and the Platteville has yet to collapse onto the St. Peter. The only reliable way to find it is to look for places where both the Platteville and St. Peter are exposed, and then check the area between them. Even then, you might not be able to see it well; for example, at Minnehaha Falls, the Glenwood is so deeply recessed you can't see much at all. The most obvious exposures are at Lock & Dam 1 and Dayton's Bluff.

Friday, December 12, 2014


Technicalities. Say you've got this thing, it's got two halves to its shell, the halves are called "valves", "bi" is two, "bivalve". Simple, right? Not so fast! There are bivalves, in the simple "it's got two half shells" sense, and then there are bivalves, in the "mollusk that belongs to Class Bivalvia" sense. Why bring this up? Aside from bivalved mollusks, we've also got another group of invertebrates with two half shells that is quite common in the fossil record, with abundant examples in the Decorah and Platteville formations. This group is Brachiopoda.