Tracking the trilobite in St. Paul

Mud at my feet, a collapsing cliff of shale above, I stoop to pick up a piece of Minnesota's long-gone past. It's a Wednesday morning in mid-October, an epic autumn day with blue sky and golden leaves, and I'm playing hooky from work with my wife and our son, Charlie, a 16-month-old propped up for the hike in a kid-carrier backpack. In a mud puddle, glinting out from a gray soup of sludge, the white fossilized form of a bryozoa has caught my eye. This tiny creature, a resident of the land we now call Minnesota, was frozen in time before the dinosaurs.

We're hiking the bluffs of St. Paul's Lilydale Regional Park, a former industrial site above the Mississippi River mined and occupied for decades by Twin City Brick Co. But since the 1980s, when the city's Parks & Recreation Department took control of the site, Lilydale has been open to the public as a little-known paleontological wonderland.

"Fossil hunting is a rare recreational opportunity," said Karen Clark, a Parks & Recreation manager.

Indeed, with a $10 permit -- available April 1 to Oct. 31 through the city (651-632-5111 or www.stpaul.gov/index.asp?NID=1560) -- amateur paleontologists can take toothbrushes and garden tools to Lilydale's fossil beds to snoop for bryozoa, brachiopods, clams, crinoids, snails, cephalopods and other creatures of the Ordovician Period, a time more than 400 million years ago when the local life looked nothing like it does today.

The exposed stone of Lilydale -- a mixture of shale, limestone and sandstone -- is the remnant of an era when Minnesota was underwater.

In Ordovician times, drifting continental plates had moved the land south of the equator, with a warm tropical sea flooding in to engulf the foundation of the bluffs that would one day overlook downtown St. Paul.

It was in this far-ago world that my little bryozoa thrived along with the innumerable sea creatures now petrified in St. Paul's sedimentary stone.

In the 20th century, mining on the bluff carved huge amphitheaters in the shale and upturned earth undisturbed for eons, scattering millions of mineralized creatures to the ground for anyone to see.

Today, school groups, museum classes, Boy Scout troops and families make the hike uphill from a parking lot off Water Street about a mile southwest from Harriet Island. As of September, the city had issued permits to facilitate fossil hunting this year for more than 5,000 people.

Our hike started in the quiet woods east of Pickerel Lake, a Mississippi River backwater at the base of the Lilydale bluffs. A switchback trail heading uphill soon led Charlie, my wife, Tara, and me to a park signboard highlighting the area's common fossil types.

A zoomed-in photograph revealed discs, half-moons and slingshot-shaped calcified forms plastered onto slabs of stone, each less than an inch in length. Knowing what to seek, we hiked away.

The hunt was on!

But our lone efforts in identification proved unnecessary, as we soon found a school group led by Karen Randall, a veteran cephalopod hunter who teaches at Expo for Excellence Magnet Elementary School in St. Paul.

As a follow-up to a science unit, Randall had organized a hands-on field trip for 120 students. They unloaded from two buses and broke into small groups, parents and teachers disappearing into the hills with kids to lead independent searches for brachiopods and other rare forms.

"I'm looking for a trilobite," said Ed McKinley, a sixth-grader standing in muck at a site marked Middle Clay Pit on the site map. "They sell for $300 at the Science Museum!"

McKinley moved a slab of shale, dredging some mud before picking up a palm-size piece.

"Cool, look at this Pac-Man guy," he said, pointing to a bump in the stone.

The group used brushes and small garden shovels. Randall pointed to spots where the kids could find fossils, and they squirted dirty slabs with water to clean them. One stone revealed dozens of mineralized remains.

"It's like a whole mess of bryozoa decided to die in the same place," Randall said.

I picked up one of the unlucky fellows, a tiny V of calcified life, and showed it to Charlie, our red-cheeked cherub in the baby backpack.

He reached out, curious, to grab the fossil, a hand grasping a piece of the past, a life form from a primordial world, forever gone but in ways still with us today.