Indiana in St. Paul

We've talked about the hobby of observing building stone before. It combines geology, architecture, and history, you can get out for a walk, and it's usually pretty cheap. Anyone who's geologically inclined has probably found themselves casting an appraising glance at a building with stonework at least once. If you make a habit of it, some kinds of stone will begin to stand out, and if you put in some historical elbow grease you'll begin to pick up on non-geological aspects. For example, if you see this in St. Paul:

The stuff in the middle of the photo, roughly weathered.

That's Platteville, and you are probably looking at a very old structure. (Well, old in St. Paul terms.) Essentially, Platteville was used as building material until better and/or more fashionable stone became available with more money and better transportation. One of the first replacements was this:

Note the bedding.

If it looks familiar, that's because we just saw the Hinckley Sandstone a few weeks back. Those quarries up at Sandstone and Banning were sending rock for buildings like this. Another major material you'll see frequently is good old Kasota stone, or the Oneota Dolomite all dressed up.

In this case rather bioturbated-looking.

Kasota stone is a perennial favorite for stonework, and is still being quarried and widely distributed. There's another perennial favorite sedimentary rock that turns up quite a bit in St. Paul, but from farther afield. It's particularly well-represented in buildings dating from around the turn of the 20th century to World War II, and once you know what to look for, you'll see it all over. It's Indiana Limestone, the trade name for what geologists know as the Mississippian-age Salem Limestone. Indiana Limestone is off-white and looks like a sandstone from a distance, with the stone frequently given a corrugated surface. Once you eyeball up to it, you'll see that the grains are actually a fine hash of invertebrate fossils.

With occasional larger bits.

With corrugated appearance, and a couple of "larger" shells.

I haven't located any large areas of coarser fossils, as I've seen elsewhere, but there are occasional pockets. One of the more westerly columns at the entrance to Union Depot has some larger bits. Net-like bryozoans are particularly tell-tale; keep an eye out when passing a building with Indiana Limestone, and you might spot small net-like patches.

This one is pretty substantial for Indiana Limestone.

Some kind of shell in cross-section near the center?

In the vicinity of Kellogg, Union Depot, the Ramsey County Courthouse, the St. Paul Hotel, the Minnesota Building, and the InterContinental all have "outcrops" at eye level. Other buildings may have them higher up, but as with natural outcrops, if they're up above your head, you're not going to get much out of them.

It's Jaws! (or not.)

A good overall sample.

The Ramsey County Historical Society publishes a book, "Rocky Roots", composed of self-guided walking tours of St. Paul building stone. (The online purchase page doesn't seem to be working, unfortunately.) I have a copy of the 1978 edition, which is generally all right for what I'm looking for because most of the buildings that use Indiana limestone are older than that, so it's not so much missing new occurrences as losing old occurrences. (e.g., if you come across a 1978 copy and want to see the brachiopods that "add delicate winged-shell patterns" to the Vermont marble of Commercial State Bank on 5th and St. Peter, you'll also have to invest in a time machine, or just stand at the southeast corner of Landmark Plaza and imagine them.)

References

Kain, J., and P. Nelson. 2008. Rocky roots: geology and stone construction in downtown St. Paul. Ramsey County Historical Society, St. Paul.

Paleontology of Scotts Bluff National Monument

Those of us old enough to have attended elementary school circa 1985–1990 may remember the experience of successfully (or less-than-successfully) traversing The Oregon Trail. Although the game certainly included a great deal of content and detail, you can play as long as you like but you'll never find a trace of a fossil in it. The people who actually used the real Oregon Trail and its counterparts did find fossils, though. One such intersection of paleontology and human history is Scotts Bluff National Monument (SCBL), which you can read about in our freshly issued paleontological resource inventory (Shaffer et al. 2026).

A former exhibit at the monument's visitor center highlighted examples of journal records. Figure 2 in Shaffer et al. (2026).

SCBL is part of a small cluster of National Park Service units that document the middle Cenozoic of the northern Great Plains. The most famous of these is Badlands National Park and its White River Group, but of course there is also Agate Fossil Beds National Monument and the younger Arikaree Group. Niobrara National Scenic River we saw last year. Wind Cave National Park also has some White River Group outcrops, and Fort Laramie (another place in The Oregon Trail) of today's Fort Laramie National Historic Site sits among Arikaree Group strata and was used by O.C. Marsh as a base of operations. Another Trail landmark, Chimney Rock, is the focus of NPS-affiliate Chimney Rock National Historic Site as well as the source of type specimens for the bird Phasianus (now Archaeophasianus) mioceanus Shufeldt 1915 and the rodent Eumys brachyodus Wood 1937. SCBL fits quite neatly among this regional crowd, complementing some of them and partially filling the temporal and stratigraphic gap between the Early Oligocene of Badlands and the Early Miocene of Agate Fossil Beds.

Click to expand for the annotations. 120 years can make a difference! Figure 5 in Shaffer et al. (2026).

The new report includes a new stratigraphic column for the monument and a detailed discussion of the mammalian biostratigraphy. Stratigraphically the monument encompasses the Oligocene part of the White River Group (Brule Formation), the mid-Oligocene Gering Formation, and younger undivided strata of the Arikaree Group. The biostratigraphy and lithostratigraphy are not quite nailed down at the top, but there is reasonable (but not conclusive) evidence that it gets into the late Early Miocene (Hemingfordian).

And if you want the technical explanation for the previous image... Figure 7 in Shaffer et al. (2026).

What kinds of fossils have been found at the monument? The great majority with solid location information come from the Brule Formation, so if you're familiar with Badlands, Scotts Bluff won't seem terribly different. There are the inevitable turtles (observed by 19th century travelers), oreodonts, and nimravids, and a whole host of ungulates. (There are only so many ways to say "small, extinct, and deer-like". It's a bit like "hypsilophodont" for any small bipedal ornithischian.) The higher stratigraphic units have not been as profuse with vertebrate body fossils as the Brule, but they do all right with trace fossils. In fact, trace fossils are one of the monument's specialties. There are vertebrate burrows in the Brule about 0.3 meter (1 foot) across and up to 4 meters (13 feet) long. One is associated with a turtle specimen. Cross-sections of animal tracks can be seen in the Gering Formation, some of which may have been made by entelodonts. Root traces and invertebrate burrows are abundant in the undivided Arikaree Group (Shaffer et al. 2026).

A number of tracks can be seen in cross-section just above the pronounced break, and the underside of one is just peeking out a little right of center. Figure 12 in Shaffer et al. (2026).

Although the people traveling by Scotts Bluff did not have time to do much more than note fossils, the site and its geologic exposures attracted geological interest. As a result, there are substantial vintage collections from "Scotts Bluff" (regrettably little other provenance information at hand) at the American Museum of Natural History, Harvard's Museum of Comparative Zoology, the Smithsonian, and especially Yale's Peabody Museum of Natural History, which has probably the longest history. At least seven fossil taxa were named from specimens found at or in the vicinity of the bluff, although only four could still be considered in use. Despite the evident interest, a comprehensive description of the site's paleontology has not been prepared until now. Scotts Bluff National Monument can take its rightful place among the paleontological parks of the Great Plains.

References

Shaffer, A. B., E. Evanoff, E. Welsh, J. S. Tweet, and V. L. Santucci. 2026. Scotts Bluff National Monument: paleontological resource inventory (public version). Science Report NPS/SR—2026/504. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2319364.

Shufeldt, R. W. 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences 19: 1–110.

Wood, A. E. 1937. The mammalian fauna of the White River Oligocene. Part II. Rodentia. Transactions of the American Philosophical Society 28(2): 155–269.