4i6 



NA TURE 



[Marc/i 4, i8S6 



west is Beteheza, a large mass of trachyte which has probably 

 welled out from an orifice on the same line of fissure from which 

 Ingolofotsy was extruded. Angavo is another of these trachytic 

 domes. One singular feature in this mountain is its numerous 

 shallow water-channels, which make their way down from the 

 summit in a surprisingly regular manner (at least on the north 

 side), giving the appearance of an opened umbrella with 

 numerous ribs. From one point of view I counted as many as 

 thirty-four of these channels. It may be mentioned in passing 

 that, in a valley at the west foot of Angavo, there is a small 

 crater whose lips are level with the surface of the ground. 

 This may perhaps be accounted for by supposing that the ejected 

 materials from this and other craters near have so accumulated 



as to raise the level of the valley between up to the rim of tlic 

 crater, and so obliterate tlie cone, probably ne\'er of any great 

 height. 



It is hardly necessary to say that these extinct volcanoes of 

 Mandridrano must have been in activity in comparatively recent 

 times. Possibly they belong to the hisioric period, though no 

 tradition lingers with regard to their being in a state of eruption.' 

 That tliey are, at any rate, of recent date, is shown by tlie 



' I was told by a native that near the village of Ambjniriana, north of 

 Angavo, and njt far from [ngolofutsy, there is an emission of gas 

 (? " fofona"), and that the people say that formerly fire was to be seen 

 The place is named Afotrona C'afo," fire ; and "trona," grunting or hard 

 breathing). 



almost perfect state of preservation in which most of the cones 

 are still found, and by the undecomposed (or but slightly de- 

 composed) character of the lava-streams that have issued from 

 them. There have been no terrestrial disturbances or modifi- 

 cations of any magnitude since the days of their fiery energy ; 

 the conformation of hill and dale was the same then as now^ 

 for, in every instance, the lava-streams have adapted them- 

 selves to the form of the existing valleys. 



Another feature worthy of mention in this volcanic district 

 is the lakes and marshes which occupy many of the valleys. 

 Itasy is the largest of the lakes, and Ifanja the largest of tlie 

 marshes. Now most of these lakes and marshes have been 

 doubtless formed by the sinking in of certain portions of the 

 district, a fact made evident by the two following circumstances : 

 — (<;) On the south side of Kasige the gneiss may be seen dis- 

 tinctly to take a sudden dip beneath the volcanic pile, showing 

 that, as the matter has been discharged from below, there has 

 been a settling down of the cone, a fact made further evident 

 by the existence of a small sheet of water, known as Bobojojo, 

 in the immediate vicinity. But (/') on the western side of Ifanja 

 marsh there is a small pond known as Mandentika. In the 

 time of King Andrianampoinimerina, about a century ago, so 

 the people say, there was a headland projecting into this pond, 

 upon which was situated a small village of t« o or three houses. 

 On a certain unhappy day the foundations of this headland 

 suddenly gave way, and down it sank with the village and its 

 inhabitants, only one of the latter escaping. From that time 

 the pond has been appropriately termed Mandentika ( " sink- 

 ing "). but previous to the catastrophe it was known as Am- 

 parihimboahangy. There is no doubt as to the truth of this 

 story, as I have myself seen traces of the submerged headland 

 and village appearing just above the surface of the water. The 

 natives of the place say that the sinking was caused by a Fanan- 

 impitoloha, a seven-headed, mythical, serpent-like monster that 

 is supposed to live beneath the water. 



Ifanja Marsh is some four or five miles from one end to the 

 other, and perhaps a mile or more wide in its greatest width. 

 It runs in a northerly and southerly direction, with its southern 

 end bending round towards the west, at the foot of which is 

 the volcano of Amboditaimamo, mentioned above. The marsh 

 is 3700 feet above the sea, forming a considerable depression 

 below the surrounding country, which is about 5000 feet in 

 altitude. At its south-eastern corner t?iere are some hot springs 

 which are much resorted to by sick folks. 



Lake Itasy covers ground, roughly speaking, to the extent of 

 about 25 square miles. It may not improbably occupy an area 

 of depression due to volcanic action ; ' but be this as it may, 

 there is a cause at its outlet sufficient to account for its formation. 

 Here, lying in the river-bed, may be seen numerous blocks of 

 gneiss, many of them blackened with a covering of oxide of 

 iron ; and beneath this gneiss lava may be seen. Several 

 volcanoes cluster round the outlet ; but there is one — an in- 

 considerable hill — situated on the southern margin of the out- 

 flowing river, just above the rapids. There distinctly enough 

 may be seen a low and much-worn crater, with its breached side 

 facing the outlet ; and gneiss blocks may be traced from the bed 

 of the river all up the hill-side to the crater. There has ap- 

 parently been first an ejection of volcanic matter, followed 

 probably by an explosion tearing up and flinging out the gneiss 

 through which the vent was bored, hence the gneiss blocks are 

 superimposed upon the lava. Thus the water has been ponded 

 back. The river has now cut its way several feet through the 

 barrier thus thrown across its course ; and by this continual 

 erosion at its outlet, and the accumulation of sediment, and the 

 growth of vegetation at its head, the lake is slowly, though 

 surely, decreasing in extent year by year. 



It seems that the lava also occupies the bed of the river 

 further down, as Mr. W. Johnson says : " Went down the Lilia 

 as far as the waterfall at Ambohipo. A more beautiful fall I 

 think I never saw. The river, broken into three streams, falls 

 in foaming white masses over an edge of black lava some 50 feet 

 deep. The whole bed of the river for a mile above is of the 



' Mr. W. Johnson says: "1 am told here that Itasy was once a huge 

 swamp, and that its becoming a clear lake is within the knowledge, or 

 perhaps the tradi ions, of the people." If this be really true, it can only be 

 e.xplained on the supposition that there has been a recent subsidence of what 

 is now the bed of the lake, as in the case of Mandentika, mentioned above. 



Mr. Sibreesays; "The natives say that the lake Itasy . . . was formed 

 by a Vazimba chieftain, named Rapeto, damming up a river in the vicinity 

 and so the rice-fields of a neighbouring chief w.th whom he was at variance 

 were flooded, and have ever since remained under water." — "The Great 

 .African Island," p. 136. 



