Students from Calvin Christian School in Blaine stand at the mouth of Echo Cave in Lilydale Regional Park. Hundreds of brown bats hibernate there during winter. (Pioneer Press: John Doman)

When I told my 6-year-old son we were going to dig for fossils, he said, "I'm going to find a dinosaur!"

Actually, we were looking for something just as unlikely —seashells in Minnesota. Millions of years ago, the Twin Cities was submerged under a shallow sea, and the marine organisms that lived on those ancient ocean floors are preserved as fossils in the bedrock. One of the best places to find traces of them is at Lilydale Regional Park, along the bluff of the Mississippi River just across from downtown St. Paul.

Anyone can enter the park, but you need a permit from the city to dig for fossils. You get there by driving along the west bank of the river past the St. Paul Yacht Club. Or you can enter at the top of the bluff, as we did, at the south end of Cherokee Park on St. Paul's West Side.

At the trailhead, we met up with Eloise Dietz, a naturalist from the nearby Dodge Nature Center. I had intended to hunt for fossils alone with my son and his friend, but I ended up being glad we had an experienced guide. The fossils are plentiful, but I'm not sure I would have recognized them on my own, even armed with the drawings I printed from a Web site.

Lilydale used to be the site of a brickyard that operated from 1894 to the 1970s and fired a buff-colored brick that was used to construct local buildings, including some on the University of Minnesota campus. Decades of mining have exposed the layers of sedimentary rock, including Galena limestone, and

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the steep, bare hillsides of gray Decorah shale. Rainfall and spring thaws washed the softer rock away, and fossils can be picked up on the surface.

We hiked down through the woods on a wide gravel trail dotted with pieces of old brick and started looking for fossils on a slope known as the east clay pit.

Dietz almost immediately picked up a gray rock the size of her thumb. On closer inspection, it resembled a thick twig covered in small dots that branched into two.

"That's a bryozoan," said Dietz, rolling the fossil in her fingers to rub off the clay. "The bryozoan was a coral-like animal that filtered food from the water. Each pore was home to one tiny animal."

My son and his friend hunched down and started poking their garden trowels into the damp clay. It didn't take them long to find something.

"Fossil alert! Fossil alert!" My son held up what looked like a closed clam shell, the size of a pencil eraser and marked by fine lines and ridges. It was a tiny brachiopod, another fossil from the Ordovician Period, 500 million to 430 million years ago.

We kept hunting and found fist-sized chunks of rock embedded with fossil fragments, including tiny "cheerios," a nickname for the rings that made up

Ninth-grader Jim Kao searches a chunk of rock for ancient marine fossils at Lilydale Regional Park. The old brickyards are a popular destination for school science field trips and community education classes. (Pioneer Press: John Doman)
the stem column of the crinoid, an ancient sea lily. I slipped one in my pocket and then became distracted by the fact that I was carrying around something millions of years old. I kept fingering it to make sure it was still there. Even though there were likely thousands of similar fossils scattered under my feet, it seemed more precious than the rings on my fingers.

We didn't find any of the more prized trilobites, an ancient relative of a crab.

"I've been with people who have found good-sized trilobites a few times," said Dietz. "But I've been coming here for 20 years, so that is a pretty rare find. Usually, we find ones that are small or broken, and you have to use your imagination to see them."

After about 30 minutes of poking around, we washed our finds in a creek and placed them in sandwich bags. Then, we explored the rest of Lilydale. We hiked a couple of minutes to a waterfall where the boys tossed sticks. We followed a path of fine white sand to the mouth of Echo Cave, formed when the brick com-pany mined the soft sandstone for bricks. Then we found Pickerel Lake. We watched the sun set while listening to crickets, grasshoppers and birds and looking over the placid water.

The next day, my son's friend took his fossils to school to show their classmates. My son put his brachiopod into his treasure box, along with his "Star Wars" action figure and Pokemon cards.

I set my tiny crinoid "cheerio" on my bedside table. It's reminding me to make the most of every day. After all, I'm going to be here on Earth for such a very short time.

Maja Beckstrom can be reached at 651-228-5295.

FAMILY OUTINGS / THE SCOOP

What: Fossil hunting at the Lilydale Brickyards

Where: Lilydale Regional Park, St. Paul

Information: Search "lilydale" at stpaul.gov for permit application, guide and maps; call 651-632-5111.

Hours: Daylight hours through October

Cost: Permits cost $10 for groups up to 10 people. If you pay by credit card, you can get a permit the day you apply.

Target audience: Elementary school age and older

Crowd pleaser: Spotting your first fossil

Tip: Bring drinking water and use restrooms before you leave home. The nearest public facilities are at Cherokee Park. Wear shoes and clothes that can get dirty. Bring a trowel, a small brush, a magnifying glass, a resealable plastic bag and tissue paper for wrapping fragile finds.

More Information: These organizations offer guided trips:

Dodge Nature Center

When: 1 p.m. Saturday l Ages: Preschool to seniors

Cost: Adults $7; children $7; families $15; free 2 and under. Register at dodgenaturecenter.org or 651-455-4531

South Washington County Community Education

When: Noon-2 p.m. Oct. 4 l Ages: 6 to adult

Cost: $15 per child (adults are free if they are with a child) Register at www.cecool.com or 651-458-6600 Science Museum of Minnesota (includes a fossil-lab session at the museum) When: 9:30 a.m.-3:30 p.m. Oct. 11 l Ages: 6-12 l Cost: $84 per child Register at smm.org or 651-221-4511