Over the Lower Magnesian

The bones of things stood out everywhere…
-Kim Stanley Robinson, Blue Mars

One of the starting points of the long process in science which led to the discovery of the Ice Ages was a very simple one: a botanist in Bavaria was looking at the moss on a rock, and it occurred to him to wonder how the rock, of a different kind from the bedrock in the area, had come to be there gathering moss. This was something a lot of people had already been wondering. Some of those people had access to Switzerland, with its glaciers, and had already realized that glaciers had considerable ability to shove rocks here and there. And some of them were starting to think that this had, at some past time, happened not just in the high mountains of central Europe, but across most of the Northern Hemisphere. Our botanist – Karl Friedrich Schimper – came to this conclusion as well. He wasn’t the first to, nor was he the one to he ultimately convince the scientific community; but he did hang a name on this episode of Earth history, not in a peer-reviewed paper, but in a poem: “The Ice Age Ode”.

Anyway, the point is: for those of us who live in places once covered by glaciation, is for the most part that a rock you see lying on the ground could have come from anywhere; most likely, a mile-high wall of moving ice scraped this off somewhere and then, roughly 20,000 years ago, dropped it in the general vicinity – in shorter terms, it’s probably a glacial erratic. It has passed through a kind of singularity, not very far back in time at all. When that rock was scraped off wherever it began existence, there were already biologically-modern human beings.

But of course, even when you can’t see them, the geological features that were there before any of the glaciers came are still down there below the erratics. Mostly you can’t reach down and pick up a piece of them, but they make their presence known. If, for example, you ride your bike north from Madison to Lodi Marsh, you find yourself, somewhere in the town of Springfield, beginning to climb up a long, shallow slope, near the intersection of Fellows Road and County Road V attaining a height with a fine view towards the Wisconsin River:
Fellows Road, on the way to Lodi Marsh State Natural Area, 10/13/13
and from there there is a downhill run, much steeper than the climb you just made; the enjoyment of coasting down it only a little tainted by the knowledge that, later on, you are going to have to get back up that steep slope. This formation, with one shallow and one steep face, is a cuesta – in this case, the Prairie du Chien Cuesta. (A little confusingly, following the cuesta westwards won’t take you to Prairie du Chien; it’s made of some of the same rock that’s found near Prairie du Chien, but that is not part of the cuesta. It’s also been called the Lower Magnesian, due to the presence of magnesium-bearing limestone; the only reference to an Upper Magnesian is in a WPA publication from the 1930s, but that also seems to refer to the Prairie du Chien Cuesta, so the puzzle persists.) Down under all the erratics, this is made of satisfyingly-ancient Ordovician rock over 400 million years old, of an age with trilobites and ammonites.

Down at the bottom of the steep face is Lodi Marsh State Natural Area. In fact it lies particularly low, because it is in a tunnel-channel, carved by water running under the glacier. Lodi Marsh has the highest documented moth biodiversity in Wisconsin, and, this presentation suggests, possibly in North America. That’s pretty cool! A sunny October day is probably not the best time to observe this. Of the hundred-odd kinds of moth found there, I saw exactly one, though in considerable numbers: woollybear caterpillars (Pyrrharctia isabella). They were at various stages of development, from little ones chewing on grass with the laser-beam focus of an ultramarathoner:
Woolybear (Pyrrharctia isabella), Lodi Marsh State Natural Area, 10/13/13
to larger ones zipping around
Woolybear (Pyrrharctia isabella), Lodi Marsh State Natural Area, 10/13/13
presumably looking for a good place to pump themselves full of natural antifreeze and pupate. Woollybears are charismatic enough that several towns have festivals honouring them; the largest in Vermilion-on-the-Lake, Ohio – which coincidentally is where I got married – where they race caterpillars and crown a Woollybear King and Queen.

Anyway, so much for moths. If the mosquitoes aren’t too bad next summer, I’ll go up again some July evening with a lantern.

It was a very warm day; I started out with several layers, which over the ride up piece by piece went into my saddlebag until it was back to T-shirt and shorts. Despite that there was no mistaking it for summer; the leaves were turning and falling, of course, and instead of the loud hum of cicadas there was the rustling of the wind in the trees. The wind was pleasant, but strong enough to make sixty-foot-high birch trees oscillate from bottom to top, and there was a note in it which could definitely turn into a howl.
Lodi Marsh State Natural Area, 10/13/13

Despite the name, the stretch of Ice Age Trail that runs through Lodi Marsh Natural Area doesn’t actually take in too much marsh. It’s cut in two by the Lodi-Springfield Road; just to the west is a steep, stepped trail that leads down to the edge of Spring Creek, beyond which you can see the marsh proper:
Lodi Marsh State Natural Area, 10/13/13

and farther along you enter a swathe of dry-mesic prairie. “Dry-mesic” – I finally take the trouble to learn, after blowing past it and similar verbiage in any number of DNR natural-area writeups – is descriptive of the moisture and drainage of a prairie, which varies along a continuum from dry to mesic to wet, with dry-mesic being intermediate between the first two. Dry-mesic prairies are not in equilibrium without fire, so to keep them in existence there have to be controlled burns. The going hypothesis around the moth diversity (according, again, to the presentation linked above; if I’m reading the slide right, it’s citing “personal communication”, so I can’t chase down any further references, plus I’m not an entomologist or ecologist anyway, so, take with grain of salt) is that the unusual transition from marsh to dry-mesic prairie – plus the nearby oak savannah – is particularly good for moths.

Even in October the prairie was full of grasshoppers and crickets, scattering with every step I took:
Field cricket (Gryllus pennsylvanicus), Lodi Marsh State Natural Area, 10/13/13

On the east side of the road the trail climbs up a hillside and plunges into some deeper woods; first oak, then birch, and then more oak. At that point the path meets a ravine and splits to left and right. The Ice Age Trail proper continues to the left. To the right, though, the trail rapidly becomes completely surrounded by ferns, both uphill and downhill, and shortly after that the ferns completely occupy the trail itself. And then there is no more trail! Just ferns. If you go left, after a ways the trail finishes up in the town of Lodi itself. To conserve energy for the ride home I didn’t walk the entire way.

The woods on the eastern leg of the trail, besides ferns, also boasted plenty of mushrooms, such as this bright yellow Pholiota on a birch log:
Pholiota sp., Lodi Marsh State Natural Area, 10/13/13

Pholiota sp., Lodi Marsh State Natural Area, 10/13/13

and also more aethalia of wolf’s-milk slime mold:
Lodi Marsh State Natural Area, 10/13/13

Near the marsh was also something that I think may be red raspberry slime mold (Tubifera ferruginosa), although quite a small specimen compared to most of the available images if so:
Lodi Marsh State Natural Area, 10/13/13

The ride back up the steep face of the Prairie du Chien Cuesta was no more fun than I anticipated. In fact, after reaching the intersection about halfway up, I just walked my bike the rest of the way. But then it was a long coast down the shallow face, back to the trail.

(Apart from Wikipedia and what’s directly linked, this post drew from Landscapes of Dane County, by D.M. Mickelson, published by the Wisconsin Geological and Natural History Survey and viewable for free online; and from Wisconsin’s Foundations: A Review of the State’s Geology and Its Influence on Geography and Human Activity , by Gwen Schultz – the second edition published 2004 by UW Press.)


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