Yol. 51.] OF A JOURNEY IN MADAGASCAR. 69 



•of Melaka (long. 48° 18' E., lat. 13° 45' S.) to that of Mahitsihazo, 

 was once flooded with trachytic lava, which, has since been largely 

 denuded, leaving patches, sometimes many square miles in extent, 

 in various places, thus allowing the underlying sandstones and 

 limestones to reappear at the surface. In other places mere blocks 

 of rock, some of them as large as small cottages, are the only 

 remnants left of the lava-bed, but those immediately north of 

 Mahitsihazo have apparently rolled down from a higher level. The 

 curiously and deeply guttered appearance of these latter blocks is 

 probably due to the action of rain alone. The trachyte varies in 

 texture from fine to coarse-grained, and in colour from buff or 

 brownish to whitish. It is in places decayed and altered into clay, 

 and is often somewhat fissile. Not infrequently it has weathered 

 into small cuboidal blocks of an inch or two in diameter, the inter- 

 stices being filled in with ferruginous matter, the blocks often 

 becoming detached one from the other and covering the ground. 

 Passing through the country in one direction only, I failed to gather 

 sufficient data as to the direction of the lava-flow to indicate its 

 source. 



A mountain named Bezavona (long. 48° 8' E., lat. 13° 55' S.), 

 probably not less than 1200 feet high, is specially worthy of 

 mention from the fact that it consists of the comparatively rare 

 rock foyaite (491), the mineral with low double refraction proving 

 to be nepheline. In long. 48° 8' E., lat. 14° 3' S., there is a hill 

 (some 10 or 12 miles south of Bezavona) known as Ankitsika or 

 Ambohibainga, probably 700 or 800 feet high. The rock is here 

 also volcanic, but in this case it is nepheline-phonolite (292, 294). 1 

 Not far from the hill of Ankitsika (some 5 or 6 miles north-north- 

 west of it) occurs an interesting form of hauyne-nepheline-phono- 

 lite with well-formed crystals of melanite (268, 314, etc.). There 

 seems to have been little, if any, actual outflow of lava from 

 Ankitsika mountain. It is of interest to note the existence of 

 foyaite, nepheline-phonolite, and hauyne-nepheline-phonolite in 

 such close association. 



The narrow promontory running north, which lies on the line of 

 long. 48° E., and forms the gulf (Port Badama in some maps) 

 at the head of which is the village of Andranosamonta, is chiefly 

 composed of basalt, being olivine-basalt (282) on its eastern edge, 

 and basalt without or with but little olivine on its western edge 

 (254). La one locality (about halfway along the length of the 

 promontory on its eastern side) I found in the basalt large nests of 

 beautifully striped onyx and multicoloured Egyptian jasper. On 

 the western side very large nodules of green chalcedony (237) 

 occur in the basalt. In the olivine-basalt of the small island of 

 Ankazoberavy, south-west of the large island of Nosibe, Egyptian 

 jasper, banded in various colours and of rare beauty, is found. 



Immediately south-west of Anorontsanga (long. 47° 58' E., 

 lat. 13° 50' S.) there are four islands (excluding islets of little 



1 Possibly some of the trachyte mentioned above may prove on further 

 •examination to be nepheline-phonolite. 



