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Madagascar
Keymaster

Their peregrination in the South Malagasy leads Raymond Decary and Urbain Faurec to the country of the Sakalava of the South, more exactly to the northeast of Maintirano. This is not far from the place where oil exploration surveys were undertaken in the first half of the twentieth century. The Tongobory dyke near Andrafiavelo pierced the Cretaceous sediments and formed over the plain, a hill of about sixty meters.
When it cooled, the basalt cracked into vertical prismatic columns.
“They recall the famous organ pipes of Espaly in the Massif Central. “Describe the two scientists.
Samples of this rock, sent to the Museum of Natural History of Paris, are recognized by Alfred Lacroix as an abnormal type of Malagasy basalt known as “Sakalavite”. It is “a hyperstene moritic basalt resulting from the consolidation of a melted and effused magma.”
The analysis carried out at the Laboratory of Mineralogy is reflected in a singular observation.
“Contrary to what is observed in these terrestrial lavas, one finds among the feldspathic meteorites great analogies with the lava which is the subject of this note, I mean the howardites and the inks,” writes Alfred Lacroix In his Note to the Academy of Sciences.
This unforeseen approximation is possible thanks to the microscope and the reagents. Thus, the small black and stony hill of Tongobory has become, from the lithological point of view, one of the most interesting scientific sites of the Great Island.
“And all this does not make one think of the rockallite of the boreal seas, whose composition is close to that of the alkaline granites of the peninsula of Ampasimena, near Nosy Be”
However, one of the main sights of the Sakalava country of Menabe is undoubtedly the silicified woods of the Morafenobe region.
“Lying on the ground, they give from a distance a singular impression of columns of temples
Killed by a cataclysm. There are some monstrous, one meter in diameter, with a length of about twenty meters. Giants overthrown and transformed into stone, they defy eternity! “
According to Raymond Decary and Urbain Faurec, the analysis shows that fossil trees are formed by quartz or chalcedony. Most often, the fibrous texture clearly remembers the primitive woody origin. Sometimes samples are seen, in which the quartz is crystallized in a rosette. “They belong to the genus Sideroxylon. “
These woods which are found throughout the Triassic region are undoubtedly floated.
It is, indeed, remarkable that they are represented only by trunks and that these are never ramified.
“Branches have been broken or destroyed during transport by currents, between the place of origin and that of deposit. “
Bongalava is sometimes referred to as the location on which these subfossil forests lived. Yet they are of the triassic age. In fact, “their presence on the surface is due to the only erosion that caused the disappearance of the sands encasing them”.
Besides, we rarely find “wood in place” in the sandstone. They exist, for example, in the banks which border the right bank of the Ranobe, downstream of the great waterfall of the river.