Yol. 51.] OF A JOUKNET IN MADAGASCAR. 67 



the sea during the interval between Cretaceous and recent times. 

 (3) Then came subsidence to the extent at least of submerging the 

 mountain-mass immediately south-east of Diego Suarez Bay and the 

 part now forming the island of Nosimitsio (probably much more). 

 {4) Afterwards elevation once more took place, but in quite recent 

 times, the low-lying country between lat. 12° 45' S. and this 

 mountain-mass being perhaps excavated (possibly by marine action) 

 during the upheaval, probably leaving the said mountain-mass for a 

 while as an island. (5) During this upheaval (probably the latter 

 part of it) the volcanic activity which brought into existence the 

 mountain of Ambohitra commenced. This seems to be shown by 

 the occurrence of the oyster-shells in the cavities of the lava at the 

 locality above mentioned, which must have been at that time at 

 or below sea-level, but which is now, as before stated, some 300 or 

 400 feet above it and 8 or 10 miles from the east coast. (6) The 

 maximum of upheaval seems to have been attained in the neighbour- 

 hood of Diego Suarez Bay, or immediately south of it ; and as the 

 north-western coast appears to have been raised to a greater distance 

 south than the north-eastern, the latter has probably experienced 

 the minimum of upheaval. 



North of Diego Suarez Bay there is a triangular headland known 

 as Baobaomby, but of this little seems to be known. So far as I 

 can make out, however, it appears to consist chiefly of limestone, 

 or limestone and sandstone, with a few extinct volcanic cones. 



V. The Noeth-west Coast and Islands. 



The more or less abrupt western edge of the great central 

 mountain-range of the island is, in the north-west (a little south of 

 lat. 13° and thereabouts), composed chiefly of brownish sandstone, 

 except at the extreme northern portion, where, as has been already 

 stated, it consists mostly of oolitic limestone. This sandstone is 

 generally of coarse texture, containing in places numerous large 

 round pebbles. The western base of this range as far as the sea is 

 mostly occupied by a belt of low-lying land, or, rather, low undu- 

 lating hills of varying width, and reaching probably nowhere a 

 greater height than 600 or 800 feet, though isolated mountains here 

 and there rise to a considerable elevation above the general level. 

 These mountains sometimes consist of sandstone — for example, 

 Angaraony (long. 48° 12' E., lat. 14° 20' S.); sometimes of 

 volcanic rocks, as Bezavona (long. 48° 8' E., lat. 14° 3' S.), etc. 

 Angaraony, which reaches an elevation of perhaps 1000 feet above 

 the ground below, with its comparatively horizontal sandstone 

 strata, stands out as a witness to the great erosion which this part 

 of the island has undergone. That the sandstones are of contempo- 

 raneous age with the limestones is shown by the fact that in certain 

 localities — for instance, a mile or two south of Andranosamonta 

 (long. 48° 4' E., lat. 14° 13' S.)— the limestones lie in beds distinctly 

 intercalated in the sandstones and conformable with these, to 



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