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Famous causeways and columns with blue basalt prisms. On the banks of the Lignon, this gigantic flow seems to want to drown us creating impressive gorges looking like organ pipes. It is said to be the most beautiful in Europe.
The lava flow: It rests partly on the coal basin (together characterized by the presence of carbon rocks) Prades-Jaujac, the other being on the crystalline base. She borrowed at the end of the course the course of Lignon who reformed his bed by incising the flow, revealing the basaltic prisms. The various stages of the organ formation (true colonnade, entablature and false colonnade) are clearly visible from the bed of the stream. Upstream of Jaujac it is possible to observe different types of rocks on either side of the river: left bank, basalt organs from the stream, and right bank, metamorphic rocks, which are rocks having changed from composition after an initial temperature change. From Jaujac, on the right bank is the casting, and left bank the metamorphic base. The lava flow, blocked downstream by the Souilhol, ebbed a few meters into the creek of La Motte, and basaltic organs are also observable. The beaches consist of alluvium, large blocks of granites and migmatites from the Lignon watershed, carried by the stream.