Introduction

Glaciations Before Glaciations Glacial Deposits Illinois Glacial Units Hydrology and History of the area

2 INTRODUCTION
    The area is located along the extreme eastern boundary of McHenry County, in northern Illinois. Archean and Proterozoic-age basement granites (Figure 2, Bedrock Geology of Illinois, Willman, 1971) are exposed at the surface in central Wisconsin and in much of central and northeastern Canada. Cambrian sandstone and shale, Ordovician sandstone, limestone and dolomite, and Silurian dolomites successively overlie the Precambrian basement rocks.
    The underlying Silurian bedrock in this area is Niagaran Dolomite. The only deposits found above the Niagaran Dolomite are from the Cenezoic Era, Pleistocene Age, and are glacial in origin. The study area lies near the northern periphery of the Illinois Basin. While the Illinois Basin was forming, surface erosion removed younger Paleozoic deposits from its periphery; these remain exposed at its center.
    Within approximately the last million years, a substantial portion of the northern hemisphere was covered by glacial ice numerous times. This occurred during a time interval that is called the Pleistocene Epoch, 1.6 million years ago. Approximately two million years ago, the Earth's surface began to cool. Ice sheets subsequently formed in regions of the sub-arctic several times; their outward spread at times covered parts of the northern hemisphere, including portions of North America and Europe.
    Four major glaciations occurred during the Pleistocene Epoch. These, from the oldest to most recent, were the Nebraskan, Kansan, Illinoian and Wisconsinan Stages. Cooler mean annual temperatures resulted in snows not completely melting. Over tens of thousands of years, major accumulations of snow compacted into ice. These eventually formed into glaciers, caused by the massive weight of the ice and snow forcing outward movement from their outer margins. The maximum extent of ice flow from this Laurentide Ice Sheet is pictured in (Figure 3 Laurentide Ice Cap, Stearn, 1979).
    On a more localized scale, tongue-shaped ice protrusions called lobes flowed in a southerly direction from Canada. These lobes converged in the central lowland area located between the Appalachian and Rocky Mountain chains. Illinois was significantly affected, because it is centrally located within this central lowland area (Figure 4 Glacial Lobes, Willman, 1971).

    Prior to glaciation, the Illinois landscape consisted of rolling hills, bisected by well-integrated drainage systems. A present-day comparison can be found in the Driftless Area within Illinois in Jo Daviess County, and also beyond the glacial limit in the extreme southern portion of Illinois. The glaciated landscapes, in contrast, have been essentially flattened beyond recognition of their earlier appearance, with the scraping of the glaciers obliterating the landforms that they traveled over, and filling in most valleys.
    It is difficult to perceive a vertical height of ice over one mile in thickness, yet that is exactly what is partially responsible for the present glaciated landscape. Sea level was several hundred feet lower, and much of this water was likely trapped within the ice from which the glaciers were formed. Large amounts of rock and soil were carried within the glaciers, often carried for hundreds of miles from the original locations from which the material was picked up.
    As the ice melted, rivers created more landforms. Those that were the fastest pathways for meltwater expanded tremendously with this erosion and sediment transport. This is especially evident in waterways that flowed toward the Mississippi River.
    Glacial drift is comprised of deposits left behind by a glacier (Figure 5 Glacial Features, Garner, 1974). A glacial deposit laid down by ice is referred to as a till. Water-laid deposits are termed outwash. Broken blocks of ice that wedge into and later melt in drift are termed kettles; most form lakes, and in some, where plant material successively accumulates concentrically, form bogs.

    When a glacier melts, till is deposited by the melting ice onto the landscape below. Water is not involved in this type of depositional environment. As a result, this sediment is stratified, or unlayered, is not sorted by particle size and shape, and varies tremendously in composition. Gigantic boulders carried by glacial ice for hundreds of miles from their origin are deposited as erratics.
    The most striking examples of till deposits are found in terminal moraines, also commonly referred to as end moraines. These deposits of glacial till are found at the outer boundary of maximum glacial extent, and can be especially pronounced when a glacial front remained static for a time. Here, the ice flow at a glacial margin was relatively constant in amount and position. The water volume resulting from melting of ice equaled the amount produced snowfall accumulation.
    Ground moraines are deposited when the ice melts or retreats, in the zone behind terminal moraines. These are also referred to as till plains. Gently undulating sheets of till characterize landscapes associated with ground moraines.
    Water-laid deposits are sorted in size and composition. This sediment is deposited in beds, layered by size as a result of gravity-influenced deposition. The coarser-sized sediment is dropped first, followed by successively finer sand and silt-sized particles. Clay-sized particles are finest in terms of grain size; remain suspended within a moving water current; these are deposited last, and sometimes very far from their original source. For example, much of the clay deposits on the margins of the Mississippi River Delta are clay-sized particles carried down by rivers whose origins are glacial. Most of the fine silt- and clay-sized outwash sediments are deposited in stagnant water bodies, such as lakes and ponds. They are also found where meltwater streams deposited sediment into a lake where an instant drop in velocity resulted in silts and clays forming delta deposits.
    On top of and within glacial ice, meltwater streams flowed and carried sediment from within the glacier. Eskers are remnants of these meltwater streams, where the heavier cobble, gravel, and sand deposits form sinuous ridges. The origin of kames is similar; these cone-shaped mounds of coarse outwash formed from where meltwater poured through ice crevasses, or into ponds on the glacier.
    Meltwater along the ice front ran off in streams. These constantly shifted and were discontinuous. The resulting broad, flat blanket of the resulting sediment, or outwash, is termed an outwash plain. Large meltwater channels that carried sediment left behind valley trains. Most outwash generated during the Pleistocene Epoch in Illinois is reflected in beds consisting of several layers of primarily gravels and sands, with lesser amounts of silts and clays. During interglacial periods, loess deposits accumulate as wind-blown silt deposits.

Glacial units within this area (Figure 6, Quaternary Deposits, Willman, 1970, & Figure 7 Illinois Moraines, Johnson, 1985) were deposited during the Altonian Woodfordian Advance by the Lake Michigan Lobe (Figure 4) of the Wisconsinan glacier. The glacier began its advance 23,000 years ago, and began to retreat 12,000 years ago. During its pulsating retreat, at least nineteen glacial moraines were built by the glacier in northeastern Illinois. It is for this reason that this region of the Illinois is physiographically described as "Wheaton Morainal Country" (Figure 8 Physiographic Divisions, Leighton, 1948). It is located within the Great Lakes Section of the Central Lowland Province of the United States, and is characterized by rugged glacial topography, with several morainal ridges, lakes, and swamps. The study area is located within the Valparaiso Morainic System, although it has been suggested by Johnson, et al. (1985) that the western border of the Valparaiso System be moved easterly to coincide with the western boundary of the Wadsworth Till. The primary till exposed within the study area is the Haeger Till. This till can only be found in northeastern Illinois. It is overlain by the Wadsworth Till to the east, and is directly underlain by the Yorkville and Tiskilwa Tills. All four of these tills are members of the Wedron Formation, which was deposited during the Woodfordian Stage of the Wisconsinan glaciation.
The Haeger Till is primarily comprised of sand and gravel, and has recently been suggested as being correlated with the Lemont Drift. The Tiskilwa, Yorkville, and Wadsworth Tills contain more clay. The Henry and Equality Formations consist of glacial outwash, and are from the earliest Wisconsinan deposition, the Altonian Substage, which preceded the Woodfordian Substage.

The local hydrology is the same now as it was after the Wisconsinan glacier retreated. The subsurface drainage patterns have remained constant although surface runoff has changed due to development inside the watershed, which has had an effect on the area.
The state of Illinois began the acquisition of the area in Moraine Hills known as Lake Defiance in 1971. In the spring of 1975, the construction of the park facilities began, and in October of 1976, Moraine Hills State Park officially opened. Moraine Hills offers a variety of plant species that have occupied this area for thousands of years. The 1,690-acre park is composed of 50% wetlands and 50% terminal moraines and hardwood forest with each area being specific to a particular type of plant species.
In 1921, Northwestern Illinois University professor W.G. Waterman was the first to log what he saw at Volo Bog. Originally Volo Bog was called Sayer Bog after the land's owner, George Sayer, a dairy farmer. In 1958, Cyrus Mark, the first director of the Illinois Chapter of the Nature Conservancy, held a fundraiser where he managed to raise $40,000 in donations to purchase the 47.5-acre bog. The area was then deeded to the University of Illinois who held ownership of it until 1970. Land developers, in the late 1960s, threatened the future of Volo Bog. Concerned citizens formed a "Save the Volo Bog" campaign that resulted in the transfer of deed to the Illinois Department of Natural Resources. In 1970, Volo Bog was dedicated as an Illinois Nature Preserve. In 1973, it was registered with the U.S Department of the Interior as a National Natural Landmark. After its registration, more than 800 additional acres were purchased to protect and enlarge the area.