SEVEN CITIES NATIONAL PARK - Piauí State
Tortoise shell - Sixth City.
This form is famous by its polygonal features, covered by lichens. The tortoise and the elephant are the most known features of this city. Both are forms covered by mostly pentagonal polygons which normally puzzles the geologist both in origin as in the formation process. Some geologists believe that these polygons are an heritage of former glacial conditions in time of deposition of sand. Fortes (1996) assumes them as contraction cracks, where the running water from rain carved ladder-like polygons. As a matter of fact, polygons are a very common feature in Sete Cidades as well in another ruinform site, the Buriti Alps, near Picos, in the central-eastern part of the Parnaiba Basin.
See more details in the GEOLOGICAL AND PALAEOBIOLOGICAL GEOTOPES OF BRAZIL where this park is described as the Geotope no 25. (Photo and description: Jorge Della Fávera - 1999).
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