Sandstone Erratic EarthCache

Erratic \Er* rat ic\, n. (Geol) masses of stone which have been transported from their original resting places by an agent of erosion (wind, gravity, water, ice).

A glacial erratic is a boulder transported and deposited by water or glaciers, having a lithology different than the bedrock upon which it is sitting.

Put even more simply, a glacial erratic is a large rock that has been dropped in a new location and now is miles and miles from another rock of the same kind.

Visit the Falls of the Ohio, in Jeffersonville, Indiana to see the largest exposed Devonian fossil beds in the world and you'll see 220 acres exposed limestone. Come to the coordinates of this EarthCache, and you see one rock that will make you ask "Now, how did that get here?"

Your “proof” might be as simple as a photo of one of the nearby smaller sandstone boulders, but there were a great many other “foreign” rocks in the general area when we were there.
If you are having trouble locating suitable material, try looking in the wash to the west of the erratic between N 38° 16.645 W 85° 45.936 and N 38° 16.653 W 85° 45.927

Within 20 feet of this location, you can find some of the fossils most often looked for at the falls.

~ Continue around the ledge to the west and go up one level to see the four foot long Siphonophretis elongata.

~ Climb the cliff just above the largest cave to see several of the best Gastropod
fossils in the park.

These layers may be covered seasonally, so do take the time to visit them if they are dry!

Glaciers, erosion, and depostion

The Earth is constantly changing. Rocks form from compacted soils, mountains grow where continents collide, and new rivers form as water seeks a path back to the sea. The process is greatly sped up by wind, water, and ice—the agents of erosion.

Erosion, transportation, deposition –those are all terms from the cycle of changes that happen to land once it has been formed. Erosion is the removal of soil, sediment, and rock from the landscape. Erosion is involved in the sculpting of hills and valleys. Erosion scours sediments from glaciated areas and transports the loose materials downslope under the force of gravity.

During erosion material is loosened, lifted, and transported. The erosion process ends when deposition of the materials in a new location begins.

Glacial ice covered the Midwest several times during the Pleistocene epoch, or the Great Ice Age. The northern two thirds of the state were completely scoured of surface materials as huge mountains of ice, some over a mile high, scraped and plowed southward.

Southern Indiana missed the effects of most of the scraping and tilling, and the resulting landscape differs from the rest of the state for that reason. However, the glaciers did have an effect on the area. While glacial ice did not extend past central Indiana, floods from the melted ice carved new rivers and created the hilly terrain of the southern third of the state.

The Ohio River as we know it did not exist before the Great Ice Ages. The Kentucky River flowed along what is now the Indiana-Kentucky border into west-central Ohio, joining the Teays River as It flowed from West Virginian into Ohio and then across northern Indiana to join the Mississippi.

About a million years ago, the first of the great glaciers pushed into the far southern latitudes, burying the Teays river under millions of pounds of clay and silt and ponding the Kentucky river until it overflowed across a divide near Madison and joined a small tributary of the Salt River.

Additional flooding and valley filling occurred as subsequent glaciers drop their heavy entrainment of till during the recessions. As meltwater spilled over the divide, the new Ohio River Valley was carved in a short period of time as water spilled and tumbled across the sand and gravels from the recent glaciers.

Once the Kentucky river joined to the upper Ohio, meltwater enlarged the stream, reversing the flow of the Kentucky river and eventually creating the Ohio River as we now know it. Proof of this is found in the relatively different amounts and types of alluvial, colluvial, and lacustrine (lake bed) deposits found along the Ohio river north toward Ohio and south toward the Mississipi . In the path of the newly formed Ohio, coarser materials are found near the source of the meltwater; gravel is abundant above Jeffersonville, but is scarce downstream.

At Clarksville, the rapids now known as the Falls of the Ohio formed as the stream cut downward through the surface material, to a small outcrop of resistant fossiliferous limestone. The falls is the only place along the 981 mile course of the Ohio River where the riverbed has cut into bedrock from shore to shore. During all this upheaval and movement of material, thousands tons of sand, gravel, rocks, and boulders joined the deposition process along the waters of the drainage basin. At some unknown point, this one large sandstone boulder was left behind, as testimony to the powerful forces of erosion.