Lock 8 North EarthCache

A short 2 mile round trip from parking to the lock and back to the parking area.

Lock 8 North is a good example of a stone lock. It has remained virtually undisturbed for the past 100 years, and is considered one of the best preserved canal locks in the U.S.

The Miami and Erie Canal was a water route that spanned about 274 miles from the Ohio River, in Cincinnati, to Lake Erie, in Toledo. Construction began in 1825 and was completed in 1845 and cost the Ohio government more than $8 milliion. After completion the canal included 19 aqueducts, three guard lock, 103 canal locks, multiple feeder canals, and a few man-made water reserviors. At its highest point was a 19 miles stretch, that expanded between New Bremen to Lockington. At this point the canal was 395 feet above Lake Erie and 513 feet above the Ohio River.

The original specifications for the locks of the Canal were that they be constructed of limestone, however this proved impractical in some areas. Where they could use limestone, it was gathered from the river beds while the rivers were temporarily damned up.

The development of St. Mary's and the surrounding region was based and continues to rely on the knowledge of eons of geological processes. The prominent features of the area are the Miami-Erie Canal and Grand Lake St. Mary's. Valuable crops are grown over glaciall-derived soils and important minerals are obtained from the unlerlying bedrock. Oil and gas production have helped shape this area and may be exploited in the future with the development of new technologies. Fossils, minerals, and meterorites, are important geological specimens that continue to be discovered in the area.

Under the glacial deposits lies the sedimentary bedrock. Dolomites, more than 400 million years old, are contained in the bedrock. A dolomite is a sedimentary rock very much like limestone, except that the calcium in limestone has been partially replaced with magnesium in a process call dolomitization. Fossils that are normally associated with shallow-marine environments reef deposits have mostly been destroyed by this process, however there are other reef attributes in the region.

Limestone is a sedimentary rock composed primarily of calcium carbonate in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris. It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or ocean water.

Dolomite originates in the same sedimentary environments as limestone - warm, shallow, marine environments where calcium carbonate mud accumulates in the form of shell debris, fecal material, coral fragments and carbonate precipitates. Dolomite is thought to form when the calcite in carbonate mud or limestone is modified by magnesium-rich groundwater. The available magnesium facilitates the conversion of calcite into dolomite. This chemical change is known as “dolomitization.” Dolomitization can completely alter a limestone into a dolomite or partially alter the rock to form a "dolomitic limestone."

Dolomite and limestone are used in similar ways. They are crushed and used as an aggregate in construction projects. They are kiln-fired in the manufacture of cement. They are cut into blocks and slabs for use as a dimension stone. They are calcined to produce lime. In some of these uses, dolomite is preferred. Its greater hardness makes it a superior construction material. Its lower solubility makes it more resistant to the acid content of rain and soil.

Dolomite and limestone are very similar rocks in color as well. They share the same color ranges of white-to-gray and white-to-light brown (although other colors such as red, green and black are possible). They are approximately the same hardness and they are both soluble in dilute hydrochloric acid. They are both crushed and cut for use as construction materials and used for their ability to neutralize acids.

As you know, Limestone and Dolomite Rock are sedimentary rocks. Sedimentary Rocks can be subdivided into four groups: Clastic, Biochemical or Biogenic, Chemical, and “other”.

Clastic
Clastic sedimentary rocks are composed of silicate minerals and rock fragments that were transported by moving fluids and were deposited when these fluids came to rest.

Biochemical
Biochemical sedimentary rocks are created when organisms use materials dissolved in air or water to build their tissue.

Chemical
Chemical sedimentary rock forms when mineral constituents in solution become supersaturated and inorganically precipitate.

“Other”
This fourth miscellaneous category includes rocks formed by Pyroclastic flows, impact breccias, volcanic breccias, and other relatively uncommon processes.

Alternatively, sedimentary rocks can be subdivided into compositional groups based on their mineralogy: Siliciclastic, Carbonate, Evaporite, Organic-rich, Siliceous, Iron-rich, and Phosphatic.

Siliciclastic
These type rocks are dominantly composed of silicate minerals.

Evaporite
This type rock is composed of minerals from the evaporation of water.

Organic-rich
This classification of rock, have significant amounts of organic material, generally in excess of 3% total organic carbon.

Siliceous
These rocks are almost entirely composed of silica.

Carbonate
These type of rocks are primarily composed of carbonate minerals.

Iron-rich,
These are composed of >15% iron.

Phosphatic
These type are composed of phosphate minerals and contain more than 6.5% phosphorus.

Weathering is the breakdown of rocks at the Earth’s surface, by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material.

There are three types of weathering, physical, chemical and biological.

Physical
Physical factors such as freezing and thawing, temperature, rain, winds, waves, water pressure and others can cause rocks to break up into tiny pieces. Specific types of physical weathering occur in specific places.
There are two main types of physical weathering:

Chemical
This is when weathering involves the reaction of some chemicals on rocks. Some rocks are more prone to chemical weathering than others. This is because some rocks readily reacts with rainwater. This chemical reaction produces new soluble substances that are easily washed away.
There are three main types of Chemical weathering:

Biological
This process of weathering is very common and we see it around us. A good example is an animal that can burrow into a crack in a rock. There are many insects, rodents and bigger animals that live in holes in the ground or rocks. Constantly, they burrow and widen cracks and end up breaking rocks apart.
Algae, lichens, bacteria and mosses often grow on rock surfaces, especially in humid regions. They produce weak acids, which convert some of the minerals to clay. Algae growth can weaken many rock types and make it more open to weathering.
Humans are no exception. Walking and construction activities like road building, mining and the like involve people ripping rocks apart. They cause weathering too.
Also importantly, weeds and plant roots can get into cracks of rocks and grow from there. As the plant grows bigger the roots grow bigger and deeper, widening cracks and splitting them apart. Decaying roots also add organic acids to the joint, speeding up the weathering process.

A near-by house is the former gatekeeper's house which is nestled among the pines. It is posted "No Trespassing."

The closest legitimate access is a two-mile round trip from either Quelihorst Road to the north, which has very limited to no parking, passing former lock 9, or S.R. 219, to the south passing where lock 7 once was.

Except for Lock 8 North, Locks 3-11 North, had been constructed of wood with little remaining. Lock 8 North is one of the few intact locks on the northern portion of the canal that is well above current water levels.

Please post a picture with your log at the posted coordinates for the waypoint "Picture Time", or as close as possible with the lock in the background.
Then you must email the answers to these questions to me.
Question 1: What is the colors of the stones in the structure at the posted coordinates?
Question 2: What subgroup would you say the stones from this structure would be part of?
Question 3: What compositional group would these stones be part of?
Question 4: Is there any evidence of weathering in the structure before you and if so to the of your ability what type of weathering is observed?

You must email me with the answers to the above questions and post your picture with your log when logging this cache or your log will be deleted.