Fox Island Alliance

Geology of Fox Island County Park

Geologic History of the Park

All of northeastern Indiana, including the Fox Island Park area, has had a long and eventful geologic history that extends far into the distant past. About 570 million years ago, an inland sea began to encroach on the North American Continent, from the Appalachian area westward to the midcontinent. The sea was warm and shallow, and provided a favorable environment for enormous numbers of sea creatures. Fossil sponges, trilobites, brachiopods, snails, cephalopods, stromatoporoids, corals, and even fish can be found in Allen County and nearby counties in rocks deposited during the Silurian and Devonian Periods of the Paleozoic Era. Typical Silurian and Devonian rocks can be seen from the viewing stand of the Hanson Aggregates Quarry along Sandpoint Road.

Younger rocks of the Paleozoic Era are found in southern Indiana, but nowhere in the State do we find rocks of the next younger major time unit, the Mesozoic Era. These missing rocks (which contain dinosaur remains elsewhere), either were never deposited as sediments in this area, or have since been removed by erosion, mostly by surface streams. Rocks of most of the next younger time division, the Tertiary Period of the Cenozoic Era, also are missing from the State of Indiana. Only one small exposure of very Late Tertiary sediments and fossils has been found in the Upper Midwest. Discovered in a quarry south of Marion in 1996, this is the only known occurrence of Tertiary sediments in this region.

The next geologic events recorded here took place during the latest part of the Cenozoic Era, the Quaternary Period, which consists mainly of the Pleistocene Ice Ages, but which also includes post-glacial time, commonly known as the Recent. During the Pleistocene, at least three major continental ice sheets advanced across the Paleozoic bedrock surface, which is approximately 50 feet beneath the land surface at Fox Island Park. The ice advances and melting left deposits of bouldery clay “till” from the ice itself, and glacial sand and gravel “outwash” from the meltwater streams. The sand dunes of the park were later shaped by the wind from sands exposed in the glacial outwash.

Geologic Features of The Park

The Sluiceway

The Fox Island Park and Nature Preserve rests in a low-lying area called the Wabash-Erie Sluiceway, because it lies between Wabash River drainage and Lake Erie drainage. Glacial sluiceways receive their name from miners’ “sluice boxes,” once used for separating gold from gravel. The Wabash-Erie Sluiceway is about two miles wide at the park, and extends all the way to Huntington, about 20 miles to the southwest. The sluiceway was eroded by meltwater derived from the most recent ice sheet that invaded this area, known as the Wisconsin Glacier. Its meltwater produced the ice-marginal St. Joseph and Ste. Marys Rivers, which then flowed through the sluiceway from Fort Wayne to Huntington, where the sluiceway stream was joined by another stream that today is called the headwaters of the Wabash River.

During glacial time, however, the stream that first occupied the Wabash-Erie Sluiceway and its tributaries were the true headwaters of the Wabash River. Since then, the tributaries (the St. Joseph and Ste. Marys Rivers) have been captured by the east-flowing Maumee River, leaving only a small “beheaded” and “underfit” stream in the sluiceway. This tiny stream, called “Little Wabash River,” or “Little River,” now begins just east of Fox Island Park and flows in a ditch along Yohne Road, just south of the park.

A good view of the sluiceway can be observed in the northwest part of the park by taking the marsh trail and climbing the viewing stand at the south edge of the marsh. The extreme flatness of the sluiceway surface is well displayed here. The low hills in the distance are the north banks of the sluiceway valley, about a mile away. In late Wisconsin glacial time, about 12,000 to 15,000 years ago, this area probably was flooded with water several feet deep during summer melting seasons.

The Sand Dunes

The most striking topographic features of the Fox Island Park are its sand dunes. Low patches of sand can be seen near the parking lot and in the field southwest of the lake, but the main dunes are in the Nature Preserve, north and northeast of the lake. Here the dunes rise 30 feet or more above the level of the sluiceway and extend about 1,000 feet along the south edge of the Preserve area. The dunes were formed after the sluiceway surface was produced, and thus have been built on the sluiceway surface. These dunes are the largest of several dune fields in Allen County. They are stabilized dunes that have been rendered inactive by the large trees and other vegetation that grow on its surface and thus prevent movement of its sand by the wind.

Size and sorting of the dune sand. A walk along the sandy trails of the Nature Preserve presents numerous features that illustrate the geologic history of the park. Along the dune trails, sand underfoot illustrates the small (“fine sand”) size and uniform size of the sand grains. Wind is the only geologic agent that can sort “fine sand” this well. The coarser pebbles from the outwash gravel source have been left elsewhere by the wind, and even finer silt and clay (dust) have been blown to other places. The remaining deposit of well sorted sand was then moved slowly along the sluiceway surface by the wind and eventually piled up here to form the dunes. The dunes are elongate in an east-west direction, and gradually decrease in height toward their west end. The dunes thus appear to be “longitudinal dunes” that probably formed parallel to a westward prevailing wind direction.

Minerals of the dunes. The sand grains of the dunes have a variety of colors, physical properties, and compositions. The most common clear, glassy grains are quartz [SiO ~2~ ] and the pink or reddish grains are garnet [Fe ~3~ Al ~2~ (Si0 ~4~ ) ~3~ ], both very hard minerals. If these grains are placed on a piece of paper and squeezed with a fingernail or pocket knife, the grains will cut through the paper, scratch the fingernail, and even scratch the knife blade. Quartz and garnet are so hard that they are used to make quartz “sand paper” and “garnet paper,” and they are so physically and chemically resistant that they will remain in the dunes for a long, long time.

The scattered black grains also have unique properties. If these grains are placed on a piece of paper, they can be isolated and dragged along the paper surface by a magnet held beneath the paper. These grains are magnetite [FeO.Fe ~2~ O ~3~ or Fe ~3~ O ~4~ ], a magnetic mineral. The magnetite grains are generally smaller than the quartz and garnet grains. Because magnetite has a higher specific gravity (weight per size) than the other grains, the wind transports the smaller magnetite grains along with the larger quartz and garnet grains.

Source of the sand. Indiana has no bedrock that could have acted as a source of the sand grains of the dunes. The source of the grains is hinted at in observations of mineral grains in the boulders in the low areas between the dunes and around Bowman Lake, described below. All of the sand grains (the quartz, garnet, and magnetite) have been weathered and/or eroded from igneous and metamorphic rocks (similar to these boulders) from the Canadian Shield, hundreds of miles to the north.

The Interdune Areas

The low areas between the dunes are relatively flat, and are underlain by dark soil. The black or brown-black soil color is from decomposed organic matter that accumulates in the poorly-drained interdune areas.

A few large boulders also are found in the interdune areas. When such boulders are transported by streams, they become rounded, but when transported by glacial ice the boulders are held rigidly and rubbed against other rocks, producing smooth, flat surfaces (facets) and long, parallel scratches. The surfaces of the interdune boulders are mostly smoothed and rounded, but some also have flat, smooth, shiny surfaces with parallel scratches, evidence that the boulders were carried into this area by glaciers and that they also were moved and shaped by meltwater streams.

In addition to the boulders in the interdune areas, other boulders are found in the glacial till of Bowman Lake and on the sluiceway surface in nearby farm fields. Many boulders can be seen piled along fence rows where I-69 and Ellison Road cross the sluiceway. Still other boulders, cobbles and pebbles are no longer present, but were ground up into sand size, mixed with other sand, then sorted and piled up by the wind into the nearby dunes. A representative collection of boulders found along Yohne Road south of the Park and donated from the nearby StoneCo Quarry are displayed in the Fox Island Geogarden, near the main entrance to the Nature Preserve. Most of these glacial boulders are igneous and metamorphic rocks transported here from Canada, but a one is a polished and striated limestone block derived from local Indiana bedrock.

The “Quaking Bog”

A few years ago, a so-called “Quaking Bog” existed in the northeast corner of the Fox Island Nature Preserve, in the lowlands just north of the dunes. During wet times of the year, jumping up and down on the bog surface would cause the surface to visibly shake or “quake.” During wet times, underlying organic matter became saturated with water, giving it a jelly-like consistency. In some bogs, plants produce an organic mat on top of water, so that it is possible to “walk on water” in such bogs.

Unfortunately, the organic layer beneath the Fox Island “Quaking Bog” is not very thick, and over the past few years a gradual lowering of the local water table has essentially stabilized the small bog. In other words, the “Quaking Bog” no longer quakes!

Bowman Lake

Bowman Lake occupies an artificial lake basin (a “barrow pit”) scooped out during construction of I-69. Soil and sediment were “borrowed” from this area to make the nearby overpass for Ellison Road.

Glacial till. Pebbles and small boulders are embedded in the clay around the margin of the lake, best exposed along the lake’s north side. This material, called “glacial till,” was deposited directly out of the ice of the Wisconsin glacier. Glacial till is a completely unsorted material, with pebbles and boulders mixed with the finest sand, silt, and clay particles. Because ice is a solid, it cannot sort materials as streams and the wind do. Midwestern till is mostly clay, and many of the clay soils of the Fort Wayne-Allen County area are derived from clay till similar to that seen along Bowman Lake.


Geological Consultant and Author: Dr. Jack A. Sunderman, Retired Professor of Geology, Indiana University - Purdue University, Fort Wayne

Fox Island Alliance Nature Publication No. 5, 1988, Revised 2003.