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Description
Outcrop located at the confluence of the streets of Arnold Schonberg, Verdi and Baixada de Briz in the southwest of Park Güell, where dark and hard rock is observed. This silicic sedimentary rock features centimetric layers of alternating dark colors with milimetric levels of clear colors. Locally, there are centimeter nodules of phosphate, light gray. This outcrop is characterized by the presence of various types of folds, ranging from loose wavy to closed folds.

The eye of the geologist
These rocks are formed by chemical precipitation from the accumulation of remains of marine microorganisms. The color variation is due to the greater or lesser amount of organic matter. The local name of these rocks is lidita and compositional level are formed almost exclusively by quartz. The accumulations of phosphates in the form of nodules are related to skeletal accumulations.

History and interpretation
These layers were deposited in a seabed environment during the Tournaisan (Carboniferous) about 350M as a result of the accumulation of billions of siliceous skeletons of unicellular organisms called radiolaris, currently extinct.
The folding and the observable deformation on the rocks, as well as its metamorphism, took place during the heretic orogenesis about 310 Ma.

Interest
The interest of these rocks is scientific because they mark the boundary between the Devonian and the Carboniferous and constitute a level of supraregional reference that can be followed by Europe, the Balearic Islands and North Africa (Algeria).

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