One of my favorite authors is the late James Michener. For years while he was alive, his fans looked forward to reading one of his thick, arm-breaking novels, especially during the summer.
From Hawaii to Texas to Alaska, Michener has entertained and enlightened. It seemed to me, at least, that Michener must have spent years researching each of his books—and he did. One of the wonderful things about all of them is the minute detail into which Michener goes in explaining the background of the story he’s telling.
In Centennial, for instance, Michener starts out by telling the story of the life of a lady brontosaurus who was galumphing around Colorado 60 million years or so ago.
Here in Kendall County, not a whole lot was happening 60 million years ago, at least we don’t think so. At that time, this part of the landscape was high, dry land of a kind that unfortunately didn’t lend itself to the preservation of fossils. So I suppose it would be more accurate to say we don’t think a whole lot was happening back then.
The real action had happened some millions of years before, starting in the Precambrian era when the Earth’s crust got its foundation. Here in Kendall County, the evidence of Precambrian times—a thick layer of granite—lies about 4,000 feet below the surface, forming what geologists like to call the Precambrian Basement. It’s sobering to think that at one time, about a billion years ago, that granite was the surface of the land, although not one we’d recognize. During that era, the area was bare, dense rock, possibly cut by a few streams with no life at all, because the oxygen we breathe today had yet to be liberated from the planet’s crust.

A nice bunch of tentaculites Oswegoensis (the elongated cone-shaped fossils) along with a nice crinoid plate is part of the exhibit at Oswego’s Little White School Museum.
From the lifelessness of the Precambrian, the area lurched into a riot of life during the Paleozoic Era starting about 570 million years ago. It was during this era that much of the dolomite and limestone that undergirds Kendall County was laid down. During the Ordovician period of the Paleozoic, from about 505 to 438 million years ago, Kendall County was part of the floor of a shallow sea. Because of this, large deposits of sandstone—particularly the valuable white St. Peter sandstone that can be found along the south Fox River—that can be found up and down the Fox Valley were left behind, as were layers of Ordovician limestone and dolomite. The numerous invertebrate creatures that thrived in the warm seas overlaying Kendall County left their mark in fossils in limestone outcrops all over the area. They can be most easily seen in my hometown of Oswego along Waubonsie Creek near North Adams Street where brachiopods and other bi-valves, along with other fossilized creatures, are commonly visible.
And, in fact, one of those creatures is even named for Oswego. As the story goes, in 1852 Dr. Mordecai Davis, an Oswego doctor, was surveying the area along the creek while engaging in his hobby of geology, when he discovered a fossil of a worm-like animal embedded in the blue-gray shale the creek had gradually eroded away. Since the creature was unknown to him, he conferred with Professor Wilbur at Aurora College, but the good professor couldn’t put a name to the fossil, either. So the sample collected by Davis was then reportedly sent to Washington, D.C. for study and eventually ended up at the Philadelphia Museum, where it was classified and named Tentaculites oswegoensis, after the place it was first found.
Chicago’s Field Museum maintains specimens of the ancient creature, but its identity is just as shrouded in mystery as it was when Dr. Davis discovered it almost 150 years ago. According to paleontologists at the museum, it is believed to be a marine worm of some kind, but that’s all that is known about it. The Little White School Museum in Oswego has some Tentaculites oswegoensis specimens of it on exhibit.
Two other eras of the Paleozoic, the Mississippian and the Pennsylvanian, are extensively represented in Illinois, though not necessarily here in Kendall County. Much of the limestone that is crushed for use on county roads and for other uses originated during the Mississippian era. And the Pennsylvanian era is responsible for the thick seams of coal that underlay much of Illinois just to the south of Kendall County.

A nice Annularia (a fern-like plant) fossil from the Pennsylvanian Era collected in the Mazon Creek area of Grundy County.
During the Pennsylvanian era, Kendall County was located on the equator, and the life forms that lived then support these findings by geologists. The beds of Pennsylvanian fossils found in Grundy and LaSalle counties are rich in tropical sea life and plants that grew along the shore. Geologists tell us that during the Pennsylvanian, the area was alternately flooded and dry, resulting in the absolute riot of plant and animal life (including Tully Monsters!) found in the era’s fossil beds. My buddy Paul and I spent a lot of time in the 1960s and 1970s hunting fossils down in the Mazon Creek area. We eventually donated our collection of 500 or so of them to the University of Wisconsin, keeping a few of the nicer specimens, including a Tully Monster each, for ourselves.
Then came the Mesozoic Era, from 245 to 66 million years ago, and that lack of dinosaurs that would probably have driven poor James Michener to distraction. In Illinois, rocks from that era are almost entirely missing, probably ground away by the glaciers that arrived during the Cenozoic Era—which is still underway, by the way. The Cenozoic Era has been a pretty exciting time, too, with the advent of mammals, the advance of ice sheets from the North Pole, and the arrival of the first humans along the Fox River. Up to 20 glaciations of Illinois took place during the era, during which some 85 percent of the surface area of the state was covered in glacial ice.
Interestingly enough, geologists no longer believe the glaciers were slow to advance and retreat. Instead, it is now believed that glaciers advanced quickly and retreated just as quickly. During the last cycle of advances and retreats, Kendall County’s familiar rolling landscape was created.
But back to our story of Oswego’s own fossil. Back in February as they were excavating the footings for the new multi-story commercial building on the block bounded by Washington, Adams, Jackson, and Harrison streets (the old Alexander Lumber Company site) excavators uncovered the layer of blue-green Maquoketa shale that extends to Waubonsie Creek. In amongst the shale—named for the Jackson County, Iowa town where it was first identified—a local fossil hunter found some nice specimens of Tentaculites oswegoensis. It was treated as quite a discovery by some of the local press and even the Chicago Trib and the Sun-Times picked up on it as the collector presented a specimen to the Oswego Village Board. The board was appropriately gratified and village officials said they were busy learning more about the fossil named after the village and were discussing plans on how it could be properly displayed.

Oswego’s Little White School Museum features the story of Tentaculites oswegoensis as part of its core exhibit.
Of course, the real surprise would have been if no examples of good old Tentaculites oswegoensis had been found in that layer of Maquoketa shale. Most kids who grew up in Oswego knew there was a great fossil-hunting spot along the banks of Waubonsie Creek and they’ve been using their fingers to dig everything from Tentaculites to crinoid plates to bivalve fossils out of some of those soft Maquoketa deposits.
And, as noted above, there have been nice examples of the fossil on exhibit at Oswego’s Little White School Museum since the early 1990s. A fine example unearthed by naturalist, environmentalist, and author Dick Young some 25 years ago is part of the museum’s core exhibit. So, Oswego village people, if you’re looking for more information on the town’s very own fossil, just contact the museum and I’m sure they’ll be happy to help you out.
Mother Nature created a land that was kind to the humans who settled it during a period of tens of thousands of years, as well as to those who continue to arrive in growing numbers in this modern age. That creation wasn’t done quickly, of course, and still provides some surprises to those who are paying attention. But then again, things of great worth are seldom achieved overnight.