TRIP TO MADAGASCAR LACROIX. 377 



The valley of the Sahatany River southwest of Antsirabe, may be 

 taken as an example. I came upon it in going over Mount Bity, a 

 long jagged ridge more than 2,000 metere high, formed chiefly of 

 white quartzites, sometimes rising vertically, sometimes bedded in 

 great slabs which are crumbled into veiy fine sand or into lai'ge 

 gi-ains of quartz, translucid and sharp. 



The Sahatany is only a small tranc][uil river, flowing into the tumul- 

 tuous Manandona with many crocodiles, the only harmful animals 

 of Madagascar. It iirigates a large valley in which there is a remark- 

 able relation between the vegetation and the mineralogical nature 

 of the soil. Tliis is essentially formed by parallel bands of quartzites, 

 mica-schists and marbles. A monotonous mantle of high gi-asses 

 conceals the first two rocks, while the limestones, bright in their 

 white nakedness, support numerous aloes (Aloe macroclada Baker) 

 whose trunks, more than a yard in height, are surmounted by large 

 boucj[uets of green leaves. These aloes with their queer shapes, sole 

 arborescent vegetable of the valley, reveal at a distance the composi- 

 tion of its soil as easily as on a geological map. 



The precious stones are all found in the pegmatite veins, inter- 

 calated between strata of metamorphosed sediments or traversing 

 intrusions of granite. These pegmatites are very heterogeneous; their 

 two essential elements, c^uartz and microcline feldspar, at times of 

 a vivid green tint, and constituting the ''stone of the amazone," are 

 of gi-eat size. Among these rocks, it is interesting to distinguish 

 two types, as well from the scientific point of view as because of their 

 practical use. In one, the quartz often has the beautiful rose color 

 that is sought after for making small ornaments. The mica, when 

 it appears,^ is that potash-mica, in great colorless sheets, the use of 

 which for portable stoves has made the mineral popular. 



Only one gem exists by itself, the beiyl,^ but its ciystals are at 

 times enormous;^ I brought back one which measures nearly a meter. 

 You should not believe, however, that these colossal-like crystals are 

 entirely transparent; the limpid portions are seen only here and there, 

 in the midst of a fissured mass, cloudy or opaque. The colors that 

 are most sought after, those of the aquamarine, are the various 

 shades ■* of blue and the sea green, but one sees also some colorless 

 varieties and yellow or rose colors; the beautiful strildng green color 

 which characterizes the emerald is unfortunately not found there. 



1 Mica Is often lacking in the gem-bearing pegmatites. The niuscovile is not worked tliere, though a 

 very good ciuality of it is found in some special pegmatites, notably in the massif of Olotsiugy, to the 

 south of Betafo. 



*I have recently found a small quantity of uncolored topaz at Ainpangabi'', 1913. 



sThese crystals of beryl are hexagonal prisms, very long on tlie vertical axis; they are very often types 

 of weak density, of which I will speak further on. 



* The stones that are most highly esteemed are those of sky-blue shade (Ampangab^, etc.) or of a very 

 special dark blue, with a black tint (Tongafeno, Fefena, etc.). 



