This is not your usual type of geocache. For one thing, there is no physical geocache for you to find. Rather, this is a special type of virtual cache known as an EarthCache.
An EarthCache teaches an earth science lesson. The cache page must include logging tasks that help teach the same lesson. Geocachers must complete the tasks before they log the EarthCache as found.
For more information on EarthCaches, see the Geological Society of America's website.
FINDING THIS EARTHCACHE
The given coordinates take you to the corner across the street from the South Tower entrance of a Milwaukee landmark: City Hall. This Earthcache focuses on the large blocks of Berea Sandstone that cover much of the first two and one half floors of the building
In order to get credit for finding the cache, it is not enough to log it below. You also must answer the following questions and message or EMAIL your answers to the Cache Owner. DO NOT place your answers in your log entry!!!
NOTE: The logging tasks require a bit more thought and effort than many Earthcaches, thus justifying the higher D rating. However, perfection is not required. A good faith attempt to fulfill the logging requirements should be sufficient.
1. What type of rock is Berea Sandstone - Igneous (rock formed when liquid magma cools), Sedimentary (rock formed when sediment is compressed and cemented together), or Metamorphic (existing rock that has been modified by heat, pressure, and/or chemical processes)? Why do you think so?
2. How would you describe the grain (clast) size of the sand and the color of the stone comprising the exterior walls on the first 2½ floors of the City Hall? Are clast size and stone color basically uniform, or do they vary substantially? What do you believe caused the color of those stones?
3. Examine a few representative sections of the Berea Sandstone comprising the smoother stones of the interior and exterior arches under the bell tower at the South end of the building. They should be easier to examine than the regular siding stones which have artificial horizontal ridges called striations carved into them. Do you notice any signs of fossils in the stone? If so, describe what you see?
4. Examine the stones comprising the arches at the base of the bell tower. Compare any difference in weathering of the stones on the outside of the building as opposed to those inside the structure. Describe what you see. Do you think this is mechanical weathering, chemical weathering, organic weathering, or some combination? Why do you think so?
Please message or email your answers BEFORE you log your find, but no need to wait for a response from me before logging your find below.
CITY HALL
Designed in the Flemish Renaissance style, City Hall was the tallest buildings in the world at the end of the 19th Century. It remained the tallest building in Milwaukee for 78 years, until the completion of what is now the US Bank Center in 1973. Feel free to take a walk around City Hall to the extent that construction does not block your way.
The City Hall cornerstone was laid on 24 February 1894 and the building was dedicated on December 23, 1895. The building rests on 2,584 pine pilings driven into the marshy soil of downtown Milwaukee. For more information on the problems with erecting a city on swampland, see the Milwaukee Is Sinking! Earthcache.
The exterior of City Hall is composed of a number of materials, any one of which could be the subject of an Earthcache. The below grade masonry is Wauwatosa limestone (or dolomite), while above grade honed-finish (flat but unpolished) gray granite extends the foundation up to the basement window lintels (the horizontal block across the top of a doorway or window opening). Columns of polished gray granite flank each entry door. The five upper floors are faced (covered) with a pink-brown face press brick manufactured by the St. Louis Hydraulic Press[ed] Brick Company. Terra cotta (kind of an unglazed pottery) figures are used throughout the building exterior to trim window openings and embellish and complement the press brick. Meanwhile, the backup brick behind the external stone or masonry consists of Milwaukee’s own Cream City brick.
Most relevant here, however, is the sandstone from the Berea formation near Amherst, Ohio, that faces the first two and a half floors of the building. Not only do those outer walls consist of Berea Sandstone, but decorative stone figures top the piers and columns around the building, and carved-in-place blocks representing eagles and cherubs anchor design elements between the first and second floors.
SANDSTONE
Sandstone is a type of clastic rock composed mainly of sand-sized (0.0625 to 2 mm) mineral particles or rock fragments. Clastic rocks are composed of fragments, or clasts, of older weathered and eroded rocks or minerals. Over time, ions in ground water form new crystalline material while precipitating or draining through the clasts. (Imagine pouring liquid glue over a pile of stones or marbles and letting it dry). The new minerals essentially cement the original grains or clasts together. Millions of years generally are required to complete the cementation process.
Creating sandstone can be seen as two stages. First, a layer or layers of sand accumulates after settling, either from water (as in the bottom of a stream, lake, or sea) or from air (as in a desert). The sand then becomes sandstone over time as it is compacted by the pressure of deposits on top of it and cemented by the precipitation of minerals within the pore spaces between sand grains.
Most sandstone is composed of quartz or feldspar (both silicate minerals). The most common cementing materials are silica and calcium carbonate. Sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black.
- An abundance of potassium feldspar often gives a pink color.
- Fine-grained, dark-colored rock fragments, such as pieces of slate, chert, or andesite, however, give a salt-and-pepper appearance to a sandstone.
- Iron oxide cement imparts tones of yellow, orange, brown, or red.
- Calcite cement imparts a grey color.
- A sandstone consisting almost wholly of quartz grains cemented by quartz may be glassy and white.
- A chloritic clay matrix results in a greenish black color.
Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids through them like a filter and are porous enough to store large quantities, making them valuable aquifers (for storage of ground water) and petroleum reservoirs.
BEREA SANDSTONE
Berea Sandstone is a type of sandstone found in parts of Michigan, Ohio, Pennsylvania, West Virginia, and Kentucky, forming two separate "basins:" the Ohio Basin and the Michigan Basin. Ohio geologist J. S. Newberry named it after Berea, Ohio, due to the extensive quarries of the stone there.
While geologists once attributed formation of Berea Sandstone to the Mississippian Age, i.e., 358.9 to 323.2 million years ago, they have since determined that it is more appropriately part of the Late Devonian period, i.e., 382.7 to 358.9 million years ago.
It is said that most of the sand forming Berea Sandstone was washed down from the north, flowing in a river from the highlands of eastern Canada and being deposited in a type of river delta where it settled and was converted over time into sandstone.
Fossils are quite rare in Berea Sandstone, although an occasional fish fossil has been found.
Berea Sandstone tends to have uniform texture over great thickness. It is up to 72 meters (236 ft) thick in Lorain County, Ohio, and up to 79 meters (259 ft) thick in Huron County, Michigan. It also is relatively easy to cut into building blocks (aka dimensional stone). It therefore has been a prized building material for over 100 years. Quarrying of Berea Sandstone began in 1830.
WEATHERING
Weathering and erosion are related but different concepts. Weathering is the process by which rock is dissolved, worn away or broken down into smaller and smaller pieces. Erosion happens when rocks and sediments are picked up and moved to another place by ice, water, wind or gravity. We just focus on weathering here.
Weathering processes sometimes are divided into mechanical weathering, chemical weathering, and organic weathering.
Mechanical weathering physically breaks up rock. 
For instance, water can get into cracks or natural pores in the stone. When water freezes, it expands, splitting the rock a little wider like a wedge. That allows even more water in and the process repeats itself, eventually splitting off pieces of rock and splitting large rocks into smaller ones.
Even absent freezing water, repeated swings in temperature, causing rock to expand when hot during the day and contract or shrink when colder at night, can weaken the surface areas and eventually cause parts to flake off. This is sometimes called Thermal Stress Weathering or Insolation Weathering. The impact of this heating and cooling cycle is enhanced by the presence of moisture in the stone.
Another type of mechanical weathering is when wind-carried bits of sand or other materials blast the sides of nearby stones, buffing and polishing them smooth. Similarly, the action of waves on the seashore or the rush of water and transported sand and sediment in streams buffs or chips away at stone and rakes the fragments back and forth into fine sand.
Chemical weathering decomposes or decays rocks and minerals. For instance, water dissolves limestone over time, albeit a very long time. Rainwater also mixes with chemicals from smog and the like as it falls from the sky, forming an acidic concoction that dissolves rock. Limestone and marble are both composed of calcite, or calcium carbonate, which acidic chemicals can dissolve easily. In the image at left, the limestone on the right side was open to rain while that on the left was not.
However, granite and sandstone, which are composed of silicate minerals such as quartz and feldspar, are more resistant to acid rain.
Organic weathering actually can represent forms of mechanical or chemical weathering or both caused by living things. Organic weathering happens when plants break up rocks with their growing roots or plant acids help dissolve rock. This can take a form as dramatic as a tree splitting boulders while growing on a stone cliff face or ivy growing up a brick wall causing the outer layer of the bricks to crumble, or as seemingly minimal as moss or lichen growing on a stone wall.
ADDED INFORMATION
The cache owner used a number of sources to locate the information provided here. There are plenty of websites available with further information on City Hall, Berea Sandstone, and weathering if you choose to Google them. For a start, you can check out the following providing basic information:
Milwaukee City Hall - Wikipedia
Berea Sandstone - Wikipedia
Weathering - Wikipedia