Ordovician Orroral EarthCache
Hidden : 8/22/2015
Difficulty:
2 out of 5
Terrain:
2 out of 5

Size: Size: other (other)

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Geocache Description:


Although today this location is 900m above sea level, between 450-500 million years ago (the Ordovician period) there was an ocean here. From nearby landmasses to the south, rivers carried sand and silt, repeatedly depositing it into deep marine troughs. Burial of the sediments and associated heat and pressure later transformed the layers into bands of sandstone and shale.

During the late Silurian period (435-425 million years ago), volcanic activity created faults. Numerous igneous granite intrusions were forced up through the sedimentary rock. With subsequent uplift and erosion, the granite became exposed as boulder piles, slopes and cliffs. Continued uplift resulted in the land being raised high above sea level.

At GZ you will find yourself on such a granite boulder. (Of course, to see the most impressive boulders, you will need to visit the top of the ridgeline 🙂.

To claim this Earthcache you will need to visit this location, answer the questions below, and send me the answers for verification using the contact details in the listing. (Some of the answers can be determined from the nearby geology sign). Once verified, you can post your log.

Additionally, you are welcome to post photos of the location, but please do not give away any of the answers.

Questions:
1. What colour is the granite you are standing on? (not the moss on top). You may need to look at some nearby granite which has recently split to get a better indication.

2. Near the highest point on this boulder, there is a 10-15cm wide seam running across the boulder - which direction does it run?

3. Of what type of rock does the seam appear to consist of?

4. What are the granites around here collectively called?

5. How many metres on average has the Orroral river cut it's way down in this valley, during the last few million years?

Additional Hints (No hints available.)

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