Resembling or relating to seaweeds of the genus Fucus.
Of sandstone: bearing seaweed-like markings.
Calcareous siltstone, Cambrian Fucoid Beds, earth.ox.ac.uk webpage
The Fucoid beds are quite variable in appearance in composition […] The rock unit got its name from the early belief that these markings were the compressed remains of seaweeds (fucoids). Now it is thought that they are the trails left by feeding creatures on the sea floor.
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