Kyle Hartshorn

The Black Hand Sandstone of Ohio

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Kyle here –

Geology is the physical manifestation of time. The rocky foundations of our planet are the consequence of billions of years of natural processes, many of which continue today. The record of this extensive history is visible not only as layers of rock, but also in what is missing. Although often unnoticeable on human timescales, steady erosion by wind, water, and ice is a tremendous force over millennia. And across millions of years, entire mountain ranges can be uplifted, ground down to their roots, and the resulting sediments compacted into rock and uplifted into mountains anew.

By definition, gorges and canyons are among the best places to view the results of erosion, often combining exposed bedrock with more superficial—but no less interesting—features carved by running water. The bedrock may also record evidence for its own intriguing origin, adding more layers to the story (pun only half intended). The American West is well known for such exposures, the Grand Canyon foremost among them, but the East and Midwest also have their share, most cutting through Paleozoic strata: Letchworth Gorge and Niagara Gorge in New York, the Kentucky River Palisades and Red River Gorge in Kentucky, and many others.

Ash Cave, a spectacular rock shelter in Hocking Hills State Park. Unlike a true cave, rock shelters represent superficial erosion of a rock body. They typically form where stronger rock overlies softer rock. The softer rock erodes more readily than the overlying rock, forming an overhang.

Ohio has a number of notable gorges, many easily accessible to visitors within regional or national parks. Clifton Gorge, in John Bryan State Park near Dayton, cuts through Silurian strata that are age-equivalent to those at Niagara Falls. Numerous small gorges and valleys near Cleveland slice through Upper Devonian, Lower Mississippian, and Lower Pennsylvanian rocks, including the great Cuyahoga Valley (and its eponymous National Park). And south-central Ohio is home to the Hocking Hills, where great sandstone cliffs form ridges, gorges, and natural bridges within a lush, relatively undeveloped forest.

The Upper Falls at Hocking Hills State Park.

Situated near the western edge of the Allegheny Plateau, about 45 miles (~70 kilometers) southeast of Columbus, the Hocking Hills expose shales and sandstones of Late Paleozoic age. Unlike the northern and western regions of Ohio, this area was not beveled flat by glaciers during the Pleistocene and thus retains a rugged topography. Hocking Hills State Park, as well as a variety of other nearby nature preserves and local parks, is the iconic centerpiece of this scenic area, a popular destination for hikers and other nature enthusiasts. The park contains numerous gorges, waterfalls, “caves”, and cliffs, all worn out of a picturesque orange to tan sandstone.

This rock is the Black Hand Sandstone. Early Mississippian in age (roughly 355 million years old), the Black Hand is a coarse, sometimes conglomeratic quartz sandstone. It is massive in nature, without many discrete beds or major changes in its consistency. However, a number of features are visible at some localities, including cross-bedding, the angled bedding of ancient ripples or dunes, and graded beds, where layers of coarse pebbles transition upward into layers of smaller pebbles and then into sand, an indication of sorting by water.

Large scale cross-bedding in the canyon walls near Old Man’s Cave in Hocking Hills State Park. Cross-beds indicate directional movement of sediment as ripples or dunes migrate over time.
Prominent liesegang banding in the Black Hand Sandstone at Clear Creek Metro Park, southeast of Lancaster and not far from the Hocking Hills.

Another common feature of the Black Hand is liesegang banding, concentric, sometimes twisty patterns of rusty staining. In contrast to cross-bedding and graded beds, which show evidence of what was going on at the time when the sand was deposited, liesegang banding formed much later, as groundwater percolated through the sandstone, carrying iron and other minerals with it. These minerals precipitated out of solution over time, forming the colorful bands. This can be seen as a form of weathering, rather than rock formation, though the distinction is rather blurred in this case as the bands can comprise lumps and stringers that are more resistant than the surrounding sandstone.

Cedar Falls at a trickle. Though deceptively calm in this photo, the falls rushes whenever there is rainfall, as evidenced by the smoothly carved sandstone channel.

A number of waterfalls that cascade through the local gorges, including the Upper and Lower Falls near Old Man’s Cave as well as the nearby Cedar Falls. These falls have cut smooth channels into the Black Hand.

A roadcut near US Highway 33 south of Lancaster, exposing the grey-ish shales, siltstones, and fine sandstones of the upper Fairfield Member of the Cuyahoga, capped by the orange basal Black Hand.

Geologists consider the Black Hand Sandstone a member of the Cuyahoga Formation. The sandstone’s lower contact is apparently erosional, with the sandstones of the Black Hand cutting down into the shales and siltstones of the Fairfield Member of the Cuyahoga Formation below. Meanwhile, the top of the Black Hand is capped by thin conglomerate, the Byrne Member of the Logan Formation. The Logan is also sandstone-rich, but less massive than the Black Hand below and may have been deposited in deeper water.

The tall cliffs downstream of Old Man’s Cave impose their shadows on the gorge below.

Several hypotheses have been put forward to explain the origin of the Black Hand. One suggests that it is a part of a great delta, deposited offshore in the shallow sea that blanketed the midcontinent during the Mississippian. Another proposes that the Black Hand is in fact a channel itself, formed in an estuary or river that carved its way through the underlying strata during a brief episode of low sea level. In either case, the relatively large and well-worn quartz pebbles and sand that make up the sandstone must have come from land to the east, near what are today the Appalachian Mountains. Research on this matter is ongoing at the Ohio Geological Survey and elsewhere.

Black Hand Sandstone in Black Hand Gorge, Licking County, Ohio. No swimming!

While Hocking Hills may be the most famous exposure of Black Hand Sandstone, it is by no means the only one. The name was coined for prominent exposures of the rock along Black Hand Gorge on the Licking River east of Newark, Ohio. (The Gorge itself is so-named for a Native American petroglyph featuring a large black hand that was once emblazoned on one of its sandstone walls; sadly, this rock art was destroyed by 19th century construction in the Gorge. The name may also be spelled Blackhand, but the split version is preferred herein.)

Thus Black Hand Gorge is the type locality of the Black Hand Sandstone, the primary place that geologists should refer to when determining what the Black Hand Sandstone is, what it correlates to, and other questions. Although the process of naming rock units is now codified by the rules of the International Commission on Stratigraphy, rock units were less rigorously defined in the 19th and early 20th century. Additionally, some localities that once provided excellent exposures are now gone, naturally weathered away, covered by vegetation, flooded, or destroyed by later human development.

The trail through Black Hand Gorge. This exposure is actually man-made, blasted in the 1800s for a railroad that once ran along the gorge. It is near a quarry complex adjacent to the natural gorge. The Black Hand Sandstone was once widely used as a building stone.

Fortunately, the Black Hand is still well exposed in its type area, easily accessible from a hike-bike trail that follows the Licking River through the gorge, passing sandstone cliffs, fallen boulders, and old quarries. In addition to the Gorge itself, nearby roadcuts afford excellent views of the sandstone cliffs to casual observers.

True Black Hand Sandstone is only exposed in Ohio. However, some other sandstones in nearby states are believed to be of a similar, perhaps even equivalent, age, including the Burgoon Sandstone of Pennsylvania and the Marshall Sandstone of Michigan. Elsewhere, such as in northern Kentucky, the same timespan is represented by shales and is much thinner. It is sobering to note that the time period that forms towering cliffs in central Ohio is elsewhere represented by just a meter or so of mud or, in others, by nothing at all.

An imposing cliff of Black Hand Sandstone along Ohio State Route 16 east of Newark, Ohio, not far from Black Hand Gorge itself.

Similarly scenic sandstone gorges are exposed throughout the Midwest, including the previously mentioned Red River Gorge in Kentucky and Turkey Run State Park in Indiana. However, these sandstones are typically younger in age than the Black Hand, often Pennsylvanian, deposited as the American midcontinent sea was shrinking into oblivion.

Massive section of Black Hand downstream of Cedar Falls in Hocking Hills State Park, probably tens of meters high. But this is nowhere to be seen when you leave the Black Hand outcrop area, perhaps evidence that its deposition was restricted to channels in a specific region.

Fossil Club Meetings

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Kyle here –

Science has a rather odd role in society. Its achievements form the very foundations of modern civilization, yet, to many, science might as well be magic, obscure and inexplicable. Popular culture tends to make scientists seem like haughty priests in an ivory tower, keepers of arcane knowledge, augurs of great portents, and babblers of dead languages and incomprehensible jargon.

Time Scavengers hopes to change that impression by showing that scientists are ordinary people and science is not as unfamiliar or unapproachable as it might initially seem. While some disciplines may have sizeable barriers to entry—think molecular biology or high energy particle physics—others are far more accessible, particularly ornithology (as “bird watching”), astronomy (as “stargazing”), and, of course, geology and paleontology (as “fossil collecting”). Indeed, these fields are indebted to hundreds of years of contributions by experienced naturalists who were amateurs in name only.

For what is an amateur but someone who takes up their passion solely for its own sake? Paleontology is often known as a “gateway drug” for science, and with good reason: it’s hard not to be entranced by immense dinosaur skeletons at a museum, or fossil shark teeth glistening on a beach, or an ancient coral reef eroding out of a neighborhood construction site. Fossils spark the imagination. Wherever there are fossils, there are people inspired to collect them.

Dry Dredgers prospecting the fossil-rich blue shales of the Upper Ordovician Kope Formation, southeast of Alexandria, Kentucky.

And wherever there are fossil collectors, chances are there is also a local fossil club. Cincinnati is one such place. Built on the banks of the Ohio River and surrounded by 450 million year old shales and limestones packed with a wealth of fossils, the city has a strong tradition of amateur paleontology. Curious locals have been collecting brachiopods, bryozoans, trilobites, cephalopods, and other Ordovician fossils from Cincinnatian outcrops since the 1800s. Many published their findings and became nationally and internationally recognized geologists.

This legacy of citizen science lives on today in the form of the Dry Dredgers. Founded in 1942, the Dry Dredgers are the oldest fossil club in the United States, having recently celebrated the 75th anniversary of their founding in April of 2017. The club was formed in close collaboration with the geology department of the University of Cincinnati, a relationship that continues to this day.

Piles of MAPS Digest, an amateur paleontological publication put out by the Mid-America Paleontology Society.

Like most other amateur paleontology societies, the Dry Dredgers has regular field trips and meetings. The latter are held on the campus of the University of Cincinnati monthly during the school year, usually on the evening of the last Friday of the month. Free and open to the public, the meetings typically follow a consistent structure.

First, a Beginners Class convenes before the main meeting, providing basic paleontological instruction to new members and children. The more experienced members also frequently show up early to socialize with their friends. Light food and drink is usually available. Collectors share their recent finds, try to identify unusual specimens, and tell a few tall tales. The desks are always piled with fossils and fossil literature, open for all to see.

At the designated time, the club President calls the meeting to order. They then proceed to introductions, where new members and visitors tell who they are, where they’re from, and what made them decide to attend the meeting. After this rigorous interrogation, the President begins the night’s entertainment with the door prize raffle, a random giveaway of small fossils, minerals, books, and other geological paraphernalia.

A snapshot from the September 2017 Dry Dredgers meeting.

Then the main program commences: a lecture by a graduate student, professor, distinguished amateur, or other interesting character. The talks are usually an hour or so in length, focusing on a particular aspect of the speaker’s research or experience. Some are travelogues, slideshows of faraway mountain ranges and mouth-watering fossil deposits. Others focus on a particular fossil or group of fossils—trilobites and echinoderms are persistent favorites. And yet others can be quite technical, delving into PhD-level research on paleoecology and taphonomy. Whatever the topic, the audience invariably grills the speaker with a host of questions at the end of the lecture.

Nautiloid expert John Catalani speaks at the September 2017 Dry Dredgers meeting, discussing the spectacularly preserved mollusk fauna of the Mifflin Member of the Platteville Formation, an Upper Ordovician rock unit exposed in Illinois, Iowa, Minnesota, and Wisconsin.

Following the lecture, the meeting wraps up with additional business. Any professional paleontologists in attendance give a report of what they are doing: papers published, students graduated, classes taught, conventions attended, and the like. Upcoming events and other miscellaneous things are announced. Then the meeting is gaveled to an end.

Some hardy members stay long after the meeting proper, socializing late into the night. Fossils are shared, bragged about, and identified. Any remaining refreshments are consumed. Plans are made for future excursions. The last people typically trickle out around 11:00 PM, tired but satisfied.

A slab of limestone containing well-preserved mollusks from the Mifflin Member of the Platteville Formation, from a locality in northwestern Illinois. A showcase specimen brought by John Catalani to the September 2017 Dry Dredgers meeting.

For more on the Dry Dredgers, visit their website at www.drydredgers.org. The site offers a feast of paleontological information as well as plenty of photos of fossils, field trips, and meetings.

Unfortunately, chances are that you may not live near Cincinnati. However, many other fossil clubs are scattered across the United States, from North Carolina to Texas to California and almost every state in between. The FOSSIL Project has compiled a list (click here) of dozens of such organizations. Chances are, there’s one near you!

A pair of upside down cheirurid trilobites, another beautiful specimen from the Mifflin brought by John Catalani to the September 2017 Dry Dredgers meeting.