At 58 miles in length, the Knobstone Trail is Indiana’s longest and most rugged hiking trail. I covered a few of those miles last weekend while my wife and I were in the area visiting her family. Following the edge of the Knobstone Escarpment, the path winds up and down hundreds of feet over knobs and ravines. From the high points it offers some great views to the east:
The Knobstone Escarpment runs along the interface between the Norman Upland to the west and the Scottsburg Lowland to the east. The Borden Group rocks in this region were deposited in a vast river delta during the Mississippian subsystem of the Carboniferous Period, between about 359 and 323 million years ago. The highlands and the escarpment are composed of resistant siltstone sediments, while the lowlands have been completely eroded down to the softer and older shale beneath.
I started hiking at the Leota Trailhead amid the siltstone that caps the hills. I hadn’t gone far before I realized these rocks harbored a variety of fossils of the marine organisms that once lived here.
Once abundant in marine environments throughout the Paleozoic Era (541 to 252 million years ago), brachiopods were decimated in the Permian-Triassic Mass Extinction.
These animals still survive today, but in most parts of the world their niche has been filled by more competitive bivalve molluscs like clams, oysters, and mussels.
Brachiopods (sometimes commonly referred to as lamp shells) differ from bivalve molluscs in a number of ways. Perhaps the most obvious regards the symmetry of the valves, the hard shells that protect the soft inner organs. Both groups of animals have a pair of these structures. In brachiopods the valves are oriented dorsally and ventrally (up and down). In bivalves they are oriented left and right.
In spite of their morphological differences, the shells of both brachiopods and bivalve molluscs are composed largely of calcium minerals. As with other animals with shells or bones, these hard mineral structures are often well-preserved as fossils.
This fossil-rich siltstone also featured beds dotted with nodules of iron minerals:
Between the siltstone ridges numerous streams had eroded their way down to the soft shale below.
Early on streams would have eroded slowly through the resistant siltstone cap rock. Fractures and other weaknesses gave water and ice a chance to begin their slow but steady work. Once worn through the hard siltstone, erosion accelerated as water and ice encountered the soft shale below.
Deposited as marine mud long ago, these sediments were later buried, compacted and hardened into shale rock. The reintroduction of water again softened the shale, returning it to the mud-like state in which it originated. I picked up a few pieces and squished them in my hand.
In spite of the cold January temperatures, there were also some interesting organisms to be found. Most notable was the greenbrier (Smilax sp., Smilacaceae) that grew densely in many areas along the trail.
These leggy thicket-forming plants bore numerous stiff thorns that made hiking a bit prickly at times.
As with other greenbriers I’ve seen, these plants had retained green leaves well into the winter.
Various ferns were also still green:
The abundant dried-up leaves made it feel like hiking in autumn.
Lichens and fungi decorated some of the fallen logs:
I even found squirming cockroach nymphs (Blattodea) among some of the rocks:
I never would have guessed Indiana could harbor a beautiful, isolated and rugged trail of this caliber. Although I only spent a few hours here, one could easily spend several days backpacking the entire length of the trail. Back-country camping is permitting along the entire length, and it seems like it would make for a great time.