The limestone rocks of this massif were formed over a hundred millions years ago, during the Jurassic period when Earth was dominated by those living creatures which could reach huge dimensions and which palaeontology named dinosaurs (fearful, gigantic lizards), a Greek origin word which would give rise to the Portuguese “sauros” were it not for the need to adapt the name to the needs of biological taxonomy. When the existence of these extinct reptiles was discovered, mid last century, the taxonomic name “sauro” had already been given to a class of fish. Although some of them were just lazy herbivores (such as the giants that left prints at Pedreira do Galinha), others, were carnivores and would not be recommended play companions. They left the mark of their passage in prints which the consolidation of the carbonated sediment preserved, fossilized. This consolidation gave origin to the limestone rocks more or less compact which then were bent and fractured by tectonic movement until they formed the vast rising block, in relation to the surrounding terrain, which include among others the Aire, Santo António and Porto de Mós mountains.

Limestone rocks are relatively soluble and permeable in small dimension pieces. Generally they become highly permeable due to the cracks and their permeability increases with the number of cracks. Rainwater infiltration in limestone environments is, generally, very intense and concentrated in the areas where cracks are denser which is associated to areas of cracks where the rocks suffer important slips, ruptures such as the ones we know are caused by earthquakes through the vibrations introduced in the crust. The Aire mountains region is particularly rich in these occurrences. The Minde or Covão do Coelho’s “latia”, for instance, are extensive depressions where the surface waters gather and only exit or entry into the interior of the limestone massif, feeding thus the underground percolation. At times it may be temporarily retained at the bottom of the basins due to permeability of residual dissolution products (terra roça). At certain times, the flow of these waters is relatively sudden and popular knowledge rightly associates it to the muddy look of the sources such as the one of the Almoáda River’s…,

…, the water as a stunning architect did not just create these sinuous underground spaces, it also decorated them. It dropped from the ceilings or walls and for each drop it left a miniscule residue of calcium carbonate dissolved in it until it formed stalactites, suspended from the ceiling which approached the stalagmites which grew from the ground until they united in columns in a magnificent set of silhouettes. Sometimes it can not be resisted the urge to humanize those raw objects and see saints, old men and old women, or the most bizarre associations. In some of these caves, the underground waterways form small (sometimes large) lakes which give a special beauty to the environment. In these lakes unusual species of fish survive which due to the lack of light are totally blind and colourless. This must not be seen as form flaws but a beautiful example of the adaptation capacity of life forms in the most bizarre environments. In any of these caves, the installed lighting as well as the set routes give value the speleological show.