The limestone buildings of Centerville, Ohio are in fact older than they look! These familiar landmarks in this southernmost part of Montgomery County are constructed of building stone quarried from rock which formed millions of years ago. Many of the early residences in this area are constructed of the Dayton limestone.
Bedrock
The world's continental areas are those areas above sea-level that we spend most of our lives on. Wherever there is soil on the continents, if you dig down you will always strike solid rock. This is bedrock and it forms the geological foundation of all regions.
The bedrock of Montgomery County is composed of sedimentary rock which is composed of fragments of pre-existing rocks, and/or the fossil remains of animals, e.g., limestone or shale (a compacted clay). Today these rocks form in lakes, river deltas, and the oceans - wherever there is a low spot so that sedimentary particles can gather together (such as sand grains, mud particles, and shells of clams, for example).
Centerville's Geological Story
Centerville's bedrock is made up of limestone and shale formed during the Ordovician Period of geologic time (approximately 440-500 million years ago) and limestones of Silurian age (formed approximately 400-440 million years ago).
Ordovician Seas
During the Ordovician Period a large marine (salt-water) sea extended across the interior part of the North American continent, covering much of Ohio, Indiana, Kentucky, Iowa, and other states. Dark gray limestones and shales formed during this time.
Silurian Seas
The Silurian seawaters then advanced and resubmerged much of the continental heartland including southwestern Ohio. Sedimentary rocks began to accumulate again, mostly limestones, but some shales, and later during the period, dolomites (a limestone with a high proportion of the element magnesium).
Dayton Limestone
For our story it is the Silurian age Dayton Formation that is the most significant geological unit) this is also known as the Dayton limestone, and Dayton "Marble" - but it is not a true marble). The significance is that this rock was quarried extensively in Centerville and surrounding communities (notably Dayton, Kettering, and the Xenia area) during the nineteenth century for building stone - the Dayton Limestone. This is typically a tan, pale cream, to white-colored rock named the Dayton Limestone because it is well developed in the Dayton area. The rock, like all limestones, is composed mainly of calcium carbonate. In addition some dolomite (magnesium carbonate) is present, giving the tan color. Some rusty patches and streaks can also be seen. These formed by the weathering of the mineral Iron Pyrite, also known as "Fool's Gold" because it can be easily mistaken for gold when it is not weathered.
It is the Dayton limestone that gives the stone houses of the Centerville Architectural Preservation District their unique character. Most of these buildings were constructed between ca. 1806-1840. In these buildings the Dayton limestone is used for virtually all of the construction apart from the wooden floors, ceilings, roofs, and interior partition walls. However, the stone is also used in very many other buildings for footings and in basements, window sills, door steps, and there are also examples of limestone horse troughs, gate posts, and mile posts.
Take a closer look at the material that some of these features are made of - are they natural stone or artificial cement? Cement tends to be much more uniform in appearance, whereas the Dayton limestone will show traces of the original layering indicating how the sediment originally accumulated layer-by-layer on the sea floor over 400 millions years ago!
Pleistocene Ice
During the Pleistocene enormous ice sheets (glaciers) covered large parts of northern North America. During the last major glacial phase, the Wisconsinan, the glacier extended over the Dayton area and on to the Cincinnati area. As the ice melted, approximately 20,000 to 17,000 years ago, it left debris, deposited as sedimentary accumulations by the melting ice or associated meltwaters. This is how much of the glacial drift that covers the bedrock in the Centerville area originated.
Local Landscape
As you travel away from the intersection of Main Street and Franklin Street notice how the ground drops to a lower level. This is because we have moved off the Silurian limestones (Brassfield and Dayton limestones) on to the Ordovician sediments below. This is geologically similar to Niagara Falls, where Silurian limestones overlie Ordovician sediments. The lowest Silurian limestones are referred to collectively as "Niagaran" to reflect this. So we have our own Niagaran escarpment (slope) in Centerville - but did you notice? - no Falls!
The resistant Brassfield and Dayton limestones in the area form higher ground (geologically known as Outliers). In these areas the bedrock is often covered by only a few feet of glacial drift making it relatively easy to dig down to the limestones to quarry them. The Dayton limestone was the preferred building material - only small amounts of the orange-colored Brassfield limestone can be seen in local buildings. It was easy to crush to use for road construction.
The Centerville Formation is a thin green clay-rich sediment only just over one foot thick - it is not suitable as a building stone. The unit was named after Centerville by the pre-eminent geologist August F. Foerste (who taught in a one-room school in Centerville, 1880-1883).
Geologic Time
The Earth's history is divided into geological periods, each one could be considered like the months in a year - except each month in the Earth's "year" would be many tens of millions of years long.
Geologists use the term "Formation" for a geological rock unit that is distinct enough to be mapped across a region.
There are two major breaks (known to geologists as unconformities) in the geologic succession exposed in the Centerville area, that between the Ordovician and Silurian Periods and that between the Silurian and the Pleistocene deposits.
You can find a complete listing of the other historic stone buildings of Centerville here.
To receive credit for this Earthcache, you must answer the following questions and send the answers to me. DO NOT POST ANSWERS IN YOUR LOG or I will have to delete it. Also, any logs which are posted for more than 3 days without submission of the answers to me will also have to be deleted. Hey, I'm not mean, I am just playing by the rules 
- What is the name of the building at these coordinates and what type of stone is it made from?
- Which mineral is the most prevalent in this type of stone?
- Which other mineral is responsible for the tan streaks in the stone?
- Locate the mineral Iron Pyrite, also known as "Fool's Gold" in the stone and describe where you found it. Did you find both "weathered" and "non-weathered" examples? (Hint: For the non-weathered, look in the steps).
- Lastly, read about the Niagaran escarpment (slope) in Centerville. What is the elevation at these coordinates? Now go to the second waypoint. What is the elevation here? What is the reason for the difference in elevation?
Optional: Post one or more cool pictures of yourself or the great area!