Sintra Batholith
“Approximately 90 million years ago, during the Late Cretaceous, a body of magma ascended, pushing up Jurassic limestone lithologies.
The batholith of Sintra; a circular intrusion composed of a dioritic gabbro outer ring and a syenitic gabbro core (see geological map), dominates the morphology of the Serra de Sintra.
Cabo da Roca is located approximately in the center of the syenite gabbro core (syenite is basically granite but with much less quartz) and was formed due to the collapse of part of this core giving rise to vertical cliffs 140 m above sea level. ”
Bibliography: Kullberg, MC and Kullberg, JC, 2000. Tectónica da região de Sintra. In: Tectónica da região de Sintra e Arrábida. Mem. Geociências, Museu Nac. Hist. Univ. Lisboa, nº 2, 1-34.
Rock types along Cabo da Roca
Starting in the North at Praia Grande and going South to Praia da Ursa we find stratified limestone and marls that vary in consistency.
At the point of contact with the Batholith of Sintra on the Praia da Ursa riverbank, we find marbles that can be climbed both on Parede das duas Cores wall and on Ursa (pyramid).
Heading south, we have cove after cove of syenite, sometimes very hard, sometimes very rotten, interspersed with veins of basalt. A syenite that is always releasing grains, a characteristic of Cabo da Roca rock.
Finally, in the extreme south we have the Cinzentos shale, with the limestone appearing again in Praia do Guincho and Cabo Raso.
