Let's start with a pair of photos, one of typical Platteville Formation fossils and the same for the Decorah Shale:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEigMFiQDOWnagilNYKnVmBajs_uG1ombYqQ8HduIBzXbaZORzZKIW4sU3KXzTgEVSMTEdD5anCwXdtdbYep-LAIt5BqRMMDEwlCPYLUs0iYwbFieDfHETHq9wrPQcADfpzbq4KB8CpNIc2X/s400/IMG_8731.JPG) |
Welcome to the Ordovician! Hope you like brachiopods! |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhvHMC1JoWeHAcXNJ00v0En-klRkEbc4a0e1yhn5a0rSZ5z7DocEbXiQrt14YiNzSsw3n4uwEIsGXTrcfO8ZLwEILBgeWm7MUkEg7R_ksYWq7in4w-buc6bHR9S3wTTH-nAuLDT5u0JpOb_/s400/IMG_0177.JPG) |
...or bryozoans and crinoids |
No points for guessing which is which. The first photo shows natural molds and casts in the Platteville, while the second shows the well-shredded fossils of the thin limestone beds of the Decorah. Now try this one:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhS7zF_y6Hm9KPjXDv-2LJnA7MnluVC10feDVLruY1wrPG0hOlr8B-hKh672yGCkTqbrKC6UB-1BHiEetvoEWLdno1OiYGTUt-VZ71vHAu7o8co1esF4RlVqNpqJnqmXwQgt5EZZq2ofLCA/s400/IMG_8726.JPG) |
No peeking! |
Despite the preservation, this piece is from the Platteville. Specifically, it comes from a bed about halfway up the Mifflin Member. Somehow this bed managed to escape the worst of the heartbreak of dolomitization, at least in a small area. Little glimpses like this show a richer picture of the Platteville fauna than we get from the natural molds and casts. (The tiny crinoid columnals are an interesting touch, as is the relative scarcity of bryozoans.)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiuxX0OuJ0E_WKlb8oPMF0xYi_Hwn4I-BHUuDWUUF7TF-bFTtU714NjJiI86kB8a-v3-wbv3Ekja5KDXObL2roo4JRNz7mCdDgtmu0UyTS6YHJj6xcmls0o1uCknCSzOu5gQMYdTBceOd9D/s400/IMG_6600.JPG) |
They're in there. It's a proper hash. |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjYz-Mg4QZx_ss4133hpJ21nx7aEInKf2jAjV_DhdBf4he1MqD0xx2ttWaBgs2f3y7w1yF4GF5RR2X7nEPwICgU0Ho0Dq1KBNOIaME_5CrvCd_FHZ2h8EPba-2aGoJ1im0sXxJBinovndel/s400/IMG_4739_crop.jpg) |
The strophomenids might be a little smaller, too. |
There are also snails,
ostracodes, and some elongate triangular things. Some of these are probably small nautiloids, others might be
hyoliths.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_o0rKXDQrLf8bORrMWQHTgmoC36KCxBW_gfHniCfQD0UdUPpaw_wRI-H97wR05Hzkh6jJIluMrk27jYqjHrKbBa0fHKfNkbY1JzrSpv8ZlJU4X3kraJJh8cnrnBFXp4977z1mPZlFq1Wa/s400/IMG_8721_crop.jpg) |
The example near the center bottom of the photo is one I suspect is a hyolith. |
There are a lot of subtleties to the rocks and faunal assemblages once you start looking!
(Also, having found a decent place to see the Glenwood up close, I've added a couple of photos to the
old post.)