Jun
05
2011

Fossil hunting season at Lilydale is here!

Scouring for fossils: (L to R) Ashley, John, and Chris search a hillside in Lilydale Regional Park for fossils.
Scouring for fossils: (L to R) Ashley, John, and Chris search a hillside in Lilydale Regional Park for fossils.Courtesy Mark Ryan
Summer seems to have finally arrived in Minnesota and that can mean only one thing: another season of fossil collecting is here. This year, due to near-record snowfall and spring floods, the St. Paul Parks department delayed issuing collecting permits for Lilydale Regional Park, one of the best fossil collecting sites in the Twin Cities. The park is located on the bluffs across the river from downtown St. Paul and is the former quarry and manufacturing site of the now defunct Twin Cities Brick Company. You can enter the park from above near Cherokee Park, or below from Harriet Island. Either way entails hiking a bit of a distance. There's a parking lot just off Water Street, and street and lot parking near Cherokee Park. Download map

Lilydale trail map: Located at the Bruce Vento Overlook near Cherokee Park.
Lilydale trail map: Located at the Bruce Vento Overlook near Cherokee Park.Courtesy Mark Ryan (photo)
The first permits for the "Brickyards" were issued last week, so a few of us from the Science Museum headed over to the park to spend some time searching for the fossilized remains of the marine life that once populated Minnesota during the Late Ordovician Period some 460 million years ago. Back then, much of the state was covered by a shallow, tropical sea, situated below the equator. Times certainly have changed.

The abundant fauna living in that prehistoric sea included reef-building bryozoans (the most commonly found fossil), brachiopods, lily-like crinoids, gastropods, horn coral, predatory cephalopods and everyone’s favorite, trilobites.

Decorah exposure at Lilydale quarries: John is dwarfed by the quarry wall at Lilydale Regional Park's West Clay Pit. The rocks exposed here are Late Ordovician in age (450-470 million years old), and contain fossils of marine life from a shallow sea environment that once covered southern Minnesota.
Decorah exposure at Lilydale quarries: John is dwarfed by the quarry wall at Lilydale Regional Park's West Clay Pit. The rocks exposed here are Late Ordovician in age (450-470 million years old), and contain fossils of marine life from a shallow sea environment that once covered southern Minnesota.Courtesy Mark Ryan
In general, there are three areas to collect fossils at Lilydale: the East, Middle, and West clay pits. Signs posted in several spots help direct you to collecting locations, but once you’re in the park you can find fossils just about anywhere.

The fossil quarries at Lilydale expose the Platteville and Decorah Formations that overlie the St. Peter Sandstone that forms the base of the bluffs found along the Mississippi. The Decorah shale here is about 90 feet thick and easily reconstitutes back into very sticky clay whenever rain or seeping ground water mix with it. But that usually won’t deter most hardened fossil hunters.

Receptaculites: John found the fossil just laying on the ground. It measures about 8 inches across.
Receptaculites: John found the fossil just laying on the ground. It measures about 8 inches across.Courtesy Mark Ryan
Multiple trilobites: Slab of Lilydale quarry shale loaded with the heads and other remains of trilobites and brachiopods. One head (cephalon) is enlarged for detail.
Multiple trilobites: Slab of Lilydale quarry shale loaded with the heads and other remains of trilobites and brachiopods. One head (cephalon) is enlarged for detail.Courtesy Mark Ryan
We had a pretty good day at Lilydale finding the usual crop of fossils, such as crinoid rings, brachiopod shells, and bryozoa branches. Chris pointed out some trilobite heads (cephalon) Ashley and I had overlooked in a couple small slabs of shale. John picked up a nice receptaculites specimen just setting on the ground. Later, while scanning the bluff, a piece of gray shale caught my eye. It was about six-inches in diameter and contained several brachiopods. But upon closer examination, I counted the remains of at least a dozen trilobites, mostly the heads of Eomonorachus intermedius.

Ordovician trilobite: Ashely displays John's fabulous find (Isotelus gigas?) from the Lilydale quarries.
Ordovician trilobite: Ashely displays John's fabulous find (Isotelus gigas?) from the Lilydale quarries.Courtesy Mark Ryan
But what my fossil possessed in quantity, John’s big find of the day overshadowed in quality. Picking through the clay piles that had slumped down from the top of the quarry since last fall, John plucked out a very well-preserved, rolled specimen of Isotelus gigas?, measuring about 1-1/2 to 2 inches across! It’s the largest trilobite I’ve witnessed come out of the Decorah. All the ones I’ve ever found were incomplete and maybe the size of a kernal of corn at best. But John’s fossil was a doozy. Unrolled it would measure a good 3 inches in length, if not more. I don’t like being outdone so I told John there’s no reason for him to hunt for fossils anymore - he’ll never find another specimen like that. But we both know he won’t be able to stop. That’s just the way fossil hunting is; there’s always the possibility of discovering a bigger and better find next time you go out.

Typical "shell hash" slab found at Lilydale
Typical "shell hash" slab found at LilydaleCourtesy Mark Ryan
Many of the Decorah fossils can be found weathering out on the surface, so you don’t need much in the way of tools. Some people like to bring a large bucket to serve as a stool while they’re in the quarries, and then for carrying out their fossils when leaving. I usually bring some plastic sandwich or freezer bags to hold smaller fossils. Some people use tissue paper or aluminum foil to wrap and protect their more precious finds. I do that sometimes. The clay pits also contain lenses of fossiliferous rock forming what’s known as "shell hash" – a chaotic jumble of fauna preserved in a matrix of limestone or shale. A rock hammer sometimes come in handy for breaking up large slabs into smaller, more portable ones, or for climbing the quarry banks.

School kids and buses swarm the Lilydale parking lot: Fossil-hunting in the quarries is a favorite extracurricular activity.
School kids and buses swarm the Lilydale parking lot: Fossil-hunting in the quarries is a favorite extracurricular activity.Courtesy Mark Ryan
If you go to hunting in the Lilydale quarries, you’ll want to bring along some water, and bug dope - mosquitoes weren’t yet a problem, but a couple wood ticks showed up. The driest parts of the quarry are of course in the sun, so if you're like me and burn easily, and don't want to spend most of your time searching in the muddier shade, it’s best to apply some sun-block lotion to your exposed skin. John also spotted several patches of poison ivy while we were scouring the West Clay Pit so you should keep that in mind, too. It’s an isolated area so be aware of your surroundings and it’s probably best to go with someone else. The quarry walls and hillsides can be unstable and treacherous. I've seen people take serious tumbles down the quarry face. Be aware, too, that there are no bathroom facilities at the quarries. There are lots of woods and bushes, though.

If you’re going to be there for a while you might consider bringing something to eat, too. Ashley brought a delicious seven-course gourmet meal for all of us to enjoy. Okay, that’s a slight exaggeration (it was only three courses), but after a few hours of intensive fossil hunting it sure tasted like one. Ashley has secured for herself a guaranteed slot in all future fossil hunting expeditions.

For information on acquiring a fossil-collecting permit for Lilydale, check out the Lilydale Regional Park permit page. Individuals and small groups of less than ten people pay $10 for a day permit. Larger groups pay more.

The Minnesota Geological Survey offers a nice information brochure about local geology, collecting, and identifying fossils at Lilydale and elsewhere around the Twin Cities. Download it here

Going home: The trail back to the Water Street parking lot
Going home: The trail back to the Water Street parking lotCourtesy Mark Ryan
I've listed a few more websites below to help get you started and make your fossil-collecting excursion to Lilydale more fun and informative. In general, hunting for fossils is kind of like fishing; you get to enjoy the outdoors, you get to occasionally make some nice catches (finds), and you get to bring them home and clean them. But best of all (besides not having to eat them), you get to boast to your friends about "netting" some sea creatures that are over 450 million years old. That, for me, is a fish story that's way more impressive than any fish tale concerning some old lunker that got away. So get out there and dig up the next great cephalopod fossil. You'll know exactly what I'm talking about.

LINKS

List of fossil sites and equipment
More trilobite info
More about horn coral
Collecting Fossils in Minnesota (previous Buzz post)
Minnesota DNR info page on fossils
Fossil Collecting in the Twin Cities
Lilydale trail map
Lilydale Regional Park
More about Lilydale Regional Park

Your Comments, Thoughts, Questions, Ideas

Mary Longfellow's picture

To participate in a hands-on geology 'scavenger hunt' or fossil dig is just one more GREAT reason to visit St Paul! The Science Museum ROCKS it, in so many interesting ways.

posted on Sun, 06/05/2011 - 10:33pm
Anonymous's picture
Anonymous says:

this is very interesting. (I'm not surprised)

posted on Thu, 06/16/2011 - 10:56am
Anonymous's picture
Anonymous says:

Wow! I love fossils! I have a small collection and I can't wait to find more!

posted on Thu, 06/16/2011 - 11:42am
bfesser's picture
bfesser says:

On the image "Decorah exposure at Lilydale quarries", did you use a strange lens? It doesn't look like the west clay pit to me... I've spent many many hours in each clay pit, and haven't been lucky enough to find even a trace of a trilobite (just the usual brachiopods, chrinoids, and bryozoans). Any advice or tips?

posted on Sat, 05/18/2013 - 5:07pm
mdr's picture
mdr says:

West Clay Pit at Lilydale
West Clay Pit at LilydaleCourtesy Mark Ryan

bfesser - the photo in question is indeed Lilydale's west clay pit. That's the only quarry I was at that day. No strange lens was involved - I was just zoomed in on John against the quarry wall. The attached photo shows a wider view of it and in the upper right you can see the top of the house whose property line seems doomed to one day become part of the west clay pit. Access to the area wasn't easy. We had to plow through a tangle of vegetation to get to it. Regarding finding trilobites: they're are plenty of fossils of them out there - particularly their molted tails (pygidium ) but finding them is mostly just a matter of luck, perseverance, and timing. The trilobite fossils featured in this post were found in a slumped pile of clay that, sometime during the winter, had fallen from higher up in the rock column. We just happened to be the first to explore it. Just keep looking, you'll eventually find one. Good hunting!

posted on Mon, 05/20/2013 - 11:04am

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