70 KEV. K. BARON GEOLOGICAL NOTES [Feb. 1895, 



note) : Ambariovaliha, Berofia, Kalakajoro, and Antanifaly. The 

 first three of these are volcanic, and are composed wholly of olivine- 

 basalt similar to that above mentioned (256. 504). The rock is 

 remarkable for the abundance of amygdules or nests of segregated 

 minerals which it contains. These amygdules are generally of 

 large size, often attaining to a diameter of a couple of feet. They 

 are frequently hollow within (geodes), and consist for the most 

 part of pure crystalline quartz, but sometimes of agate, onyx, or 

 green (237) or brown chalcedony (501). Occasionally well- 

 crystallized calcite, generally whitish, sometimes olive-green, accom- 

 panies the quartz, and is also often found filling fissures in the 

 rock. 



The island of Antanifaly, however, which is the westernmost of 

 the group, consists entirely of Nummulitic Limestone, in which 

 Assilina spira, de Roissy, and several species of Nummulites (see 

 Mr. R. B. Newton's paper) are the commonest fossils. About 30 

 miles or so north of these islands (lat. 13° 30' S.) there are three 

 islets near the mainland : Kivonjy, Antsoha, and Ankazoberavy, 

 the last two, and probably also the first, being volcanic, the rock 

 again being olivine-basalt, which on Antsoha is columnar, the 

 columns, however, being much bent and irregular. Kivonjy is a 

 round beehive-shaped islet, the rock of which, from a distance, has 

 a whitish colour. It may possibly be trachyte. 



Farther north again is the large island of Nosibe, which is in 

 the possession of the French. This island is for the greater part 

 dotted over with volcanic cones of no great height, which are in a 

 fair state of preservation. There are two fine crater-lakes on its 

 southern edge. The only specimen of the rock which I gathered 

 from this island proves to be nepheline-basalt (265). 



Another island, Nosimitsio, farther north again (long. 48° 35' E. y 

 lat. 12° 52' S.), which, however, I have not seen, is also volcanic. 

 On the east coast of this island there are said to be some fine 

 exposures of columnar basalt, and, as was mentioned before, shells 

 have been here gathered at a height of 200 or 300 feet exactly 

 corresponding to those lying on the shore. 



Thus we see that, while trachytic and phonolitic lava has been 

 poured out in great quantity in the north-western part of Mada- 

 gascar, basaltic lava has been erupted in equal, if not even in greater 

 measure ; and that, while trachyte seems to be confined to the 

 mainland not far from the sea, basalt occupies parts of the coast- 

 line of the same, and apparently forms, with the one exception 

 already mentioned, all the islands in the region. Basalt is not, 

 however, entirely absent several miles inland, as it may be picked 

 out of the beds of some of the rivers immediately below the western 

 declivity of the central mountain-chain, as, for instance, close to- 

 the village of Ankaramy, about 20 miles from the coast. 



On the sea-coast at Ambodimadiro (long. 48° 14' E., lat. 1 3° 

 37' S.) a goodly number of dykes of a rather anomalous basalt 

 make their appearance (see description by Dr. Hatch in Quart. 

 Journ. Geol. Soc. vol. xlv. 1889, p. 345), reminding one of those 



