ANCIENT WALLS EarthCache
Hidden : 11/29/2011
Difficulty:
3.5 out of 5
Terrain:
3 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

This cache will take you on a walking tour of downtown Portland illustrating many different kinds of stone from a variety of locations and geologic periods. A hand lens or magnifying glass will let you take in even more of the beauty of these stones.

Information is courtesy of the Geological Society of the Oregon Country (see above related web page).
The Geological Society of the Oregon Country (GSOC) is a non-profit organization based in Portland, Oregon. The society is dedicated to the study of geology in the Pacific northwest and is open to persons with all levels of education and professional backgrounds.

The listed coordinates will take you to the NW entry to Pioneer Place mall. Enter and go down the escalator to start at the fountain downstairs. Permission has been given by the property manager for this waypoint as long as we " follow the rules of conduct required here as are all members of the public".

1. Pioneer Place (Built 1990) The beige floor and wall tiles at Pioneer Place contain many gastropod (snail) and pelecypod (clam) fossils. We have also found at least one Coral (cnidarea) or moss animal (bryozoa) in the food court.
The tiles appear to be Comblanchien limestone of Jurassicage,199-145 million years ago (Mya).(Comblanchien is in the Burgundy region of France.) Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate(CaCO3). Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera. Limestone makes up about 10% of the total volume of all sedimentary rocks.The wall near the escalator at the S.W. 5th and Taylor entrance is especially fossil rich. My favorite fossils can be found downstairs near the restrooms to the left of the bench. Check them out! Also, the black limestone tiles contain tiny star-shaped crinoid(5-sided columnal Sea Lily)fossils best seen on the polished bollard caps at the atrium fountain in northwest section of the mall.

2.Standard Insurance Center(1968) The walls around the Standard Insurance Center are granite.By definition, granite is an igneous rock with at least 20% quartz by volume. This granite contains quartz, augite, and large Carlsbad twin feldspar crystals (looking like connected mirror images)that show their cleavages very clearly when viewed from opposite angles.
Count Von Svoboda’s fountain statue “The Quest” on the west side is made of white Pentelic marble of Mt. Pentelikon, Greece where the marble from the Parthenon was quarried. This is the first metamorphic rock on the tour; marble is metamorphosed limestone or other sedimentary carbonate rocks. The white color indicates very few non-carbonate impurities.

3. Gus Solomon Courthouse (1933) The walls of this former federal courthouse are sandstone. This is the second type of sedimentary rock encountered on the tour. The north side has many excellent examples of both cross-bedding (internally composed of inclined layers) and exfoliation (surface-parallel fracture systems in rock which often lead to erosion). Cross beds form from running water. As the water flows, it creates bedforms, such as ripples or dunes, on the floor of the channel. Sediment deposited on the downcurrent side of these bedforms is deposited at an angle--not horizontally. If preserved, the layering is also inclined and dips in the direction of water transport.

There is a loggable benchmark to the right of the entrance (RD0441).

4. Schnitzer Concert Hall (1928) Various green and brown marbles are visible at the front of the building, including the box office. The veining is due to impurities such as sand, mud, clay, and iron oxide. Green may indicate the presence of serpentine.


5. First Congregational Church (1891) Our only Northwest natives, igneous Oregon Basalt and sandstone from Tenino, Washington make up the walls of the First Congregational Church. Large translucent calcite crystals are visible in the marble pillars at the front of the church.


To log this cache please email me your answers to the following:
1)At Stop #1 - Describe one of the fossils you see. What type of animal do you think it was?
2)At Stop #2 - How many pieces of marble were used in the statue?
3)At Stop #3 -What form does the exfoliation typically take? What do you think this says about how the blocks were cut out of the bedded stone?
4)At Stop #4 - What is the round ornament around the corner just to left of the entrance and over the display case made of?
5)At Stop #5 - Are the replacement pilasters on the sides of the entrance the same material as the central ones? If not, what do you think they are made of?

Additional Hints (No hints available.)



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