A migmatite is a heterogeneous ultrametamorphic rock, which has both igneous and metamorphic rock properties. It is formed as a result of partial melting (called anataxis), which occurs when an existing rock is subjected to high pressure and temperature conditions. Its occurrence in this area of the Natural Monument of the Alcantilado de Montedor marks the contact between the Plutonite of Bouça de Frade and the embedded metasedimentary rock that testifies the metamorphic conditions attributed to the second phase of Varisque deformation.

Prehistoric tomb that is located at the north entrance of the parish, this being one of the megalithic monuments found closest to the coast, until today. The Mamoa of Eireira is a megalithic funerary monument that was discovered by the team of the archaeologist, Eduardo Jorge and with the collaboration of the N.A.I.A.A., being one of the best conserved and most important monuments in the Northwest Peninsular. Some paintings were found and a stone was removed, which is on display at the Museological Museum of Afife. Eireira's tumulus is undoubtedly the most significant manifestation of the Neolithic in Afife. It has a diameter of 28 m and what remains is made up of 16 pillars, which define an undifferentiated “V” shaped monument.

One of the most important characteristics, in terms of megalithic typology, is the fact that the pillars considered as “halls” are of the same height as those that constitute the chamber.

The monuments of this type, also known as "Dolmens" were tombs of collective burials, which developed from the Neolithic to the Early Bronze Age, that is to say from the fifth to the second millennium before Christ.

Small quadrangular “constructions” where dry sargassum are still stored today. The roof is made with thatch and secured with roof weights of granite or schist, as in the old Castro houses. These haystacks belong to Senhora Céu Arezes, from the parish of Castelo de Neiva, one of the last sargassum gatherer that is still active.

Accordingly to Carvalhido (2008) the main distinctive features of the Local Natural Monument of Magmatic Drops in Canto Marinho landscape, of medium scale, such as granitic balls, and of detail, such as mineralogical varieties or folds, are due to the first stages of the closing of the primitive ocean, the Rheic (the records of its biodiversity and dynamics can be seen in the Local Natural Monument of Rheic Remains in Pedras Ruivas), initiated about 400 million years ago.

The crenulations and folds, also in sheaths, which give a sinuous undulation to the whitish-yellow rocks that make up much of the local substrate (quartzite), were generated in the margin lands, in the first collision phase of the primitive continents, by shortening the space, heating and dragging.

With the new impulses, the amalgamation originated the fusion of rocks and the formation of magma whose cooling, at several kilometres of depth, originated the granites that currently form the hills of St. Luzia and Arga, but also the elevation of the coastal hills of Montedor and Gelfa.

Migrating like hot air balloons through the quartzite, giant drops of magma flowed from the main magma chamber that originated Montedor (Local Natural Monument of Ancient Beaches of Alcantilado de Montedor), and through fractures consolidated here, at about 700 m.

After about 300 million years of erosive processes and tectonic uplifting, we can see the minerals witnessing the hot contact of magma (contact metamorphism) such as garnet and staurolite, and the granite balls, some with more than 10 tons, which were interpreted as a deposit (tsunamite) generated by the oldest tsunami recorded in the Portuguese seismic catalogues, from 66 BC (Baptista & Miranda, 2009).

References:

Baptista, M. & Miranda J. (2009). Revision of the Portuguese catalog of tsunamis. Natural Hazards and Earth System Sciences, 9, pp. 25-42

Carvalhido (2018). Livro de Pedra, Monumentos Naturais Locais de Viana do Castelo – Catálogo. Câmara Municipal de Viana do Castelo, 2ª edição

The Lima River to Serra de Arga Equestrian Trail and the Serra de Arga Equestrian Trail, the latter circular in character, are two itineraries created under the project "Vilas e Aldeias Equestres entre Arga e Lima", which complement the already existing regional network of equestrian trails (see: www.garranos.pt).

These two routes provide a stimulating experience of immersion in nature, of contemplation of a multifaceted landscape mosaic, of adventure, exploration and discovery of the evolution of this territory over time.

Starting from the refreshing serenity of the Lima river margins, in the remarkable parish of Lanheses, we invite you to accept the challenge of climbing to the remote and genuine village of Cerquido, on the southern slope of the Arga mountain range, a mountainous system where herds of half-forbidden chamois live.

From the village of Cerquido you can continue your journey of discovery on horseback, taking the Equestrian Trail of the Serra de Arga, a circular route that surrounds this entire mountainous massif, following, through rural and grazing paths, the main mountain villages: Arga de Cima, Arga de Baixo, Arga de São João, Dem and, finally, Montaria.

Datasheet - Equestrian trail from Lima River to Serra d'Arga

Distance: 36 km

Difficulty level: Easy

Category: Circular

More information: https://destinoequestre.pt/pt/grupos/percursos

Route in KMZ format for download: PE Serra d'Arga