| Basic Principle
A layer is more recent than the one it covers and it is older than the one that covers it.
This staircase which climbs on the bank of the Maine makes it possible to observe the contact between two layers of rocks, one that appears near the road on bank and the other at the level of the small platform. These two layers date from the Ordovician.
These sedimentary rocks were formed in horizontal strata and subsequently wrinkled. They are found in more or less eroded synclines and anticlines.
Synclinal et anticlinal
On this small platform overlooking Maine river and the road on the bank, you are on the bait of an anticline that goes up south. The syncline descends to the north under Maine
An anticline (A) and its associated syncline (B) are schematically represented here. </ P> On the eroded edge of this syncline, we can see the different strata that have stacked since the dawn of time. Here, between the road and this platform, we can see two layers of rocks, one of arkose and the other of shale slate.
The schists are metamorphic rocks formed under strong conditions of pressure and temperature. These schists date from 460 million years ago to the Ordovician and are derived from the transformation of compacted ocean clays, gradually metamorphosed into very pure schist.
These arkoses are sandstones. Their full name is arkose from Bains, because this type of rock was defined at Bains-sur-Oust near Redon. As the slate shale dates from the Ordovician. Arkose is a detrital rock rich in quartz (up to 60%), feldspath (at least 25%), often a few micas and clay (about 15%) . But it has the originality of being a coarse grained, feldspathic sandstone. Moreover, its binder is clayey, and not calcareous, which increases its resistance in time to rain.
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To valid your visit:
- 1-.What is the formation period of the 2 rocks seen here? (shown in text)
- 2-. Using the attached photos to recognize the two rocks and observing the superposition of the strata, which is the oldest?
- 3-. Optional, attach a photo of you with the hotel of the King of Poland in the background.