30 A PLUTONIC VALLEY. 



a vast rent and depression had been made across the lines of 

 hills in a diagonal direction ; while the water- worn and wasted 

 remains of some few of these towards the south, forming a 

 line of low detached hills, suggested that probably the action 

 of water, either as an arm of the sea or a great river, had 

 completed what was commenced by more violent agencies. 

 The evidence of former volcanic action in the presence of 

 extinct craters and lava streams to the west, north, and 

 north-east of the plain, gives considerable support to this 

 supposition. 



About a hundred miles north of the Antsihanaka pro- 

 vince there seem to be further traces of volcanic action. The 

 Eev. J. A. Houlder thus describes a remarkable valley called 

 Mandritsara, which, until he saw it in 1876, was unknown 

 to Europeans even by name, and not marked upon any map : 

 " It is a great basin, or rather a mighty elongated pit, sunk 

 deep down among the surrounding heights. It is about thirty 

 miles long, and nearly 2000 feet below the level of the 

 country east and west of it. Dante would have imagined 

 it, not a ' circle ' certainly, but a remnant of some region of 

 the horrible pit itself, which for a wise and gracious purpose 

 had been gently touched by the cooling breath of heaven. 

 There had evidently been a great commotion going on there 

 in the ages gone by, for all the long valley was dotted with 

 rounded hills, giving it the look of boiling water or bubbling 

 pitch, which by some strange process had suddenly become 

 concealed." 



It will therefore be seen that igneous agency has been a 

 powerful factor in shaping the physical geography of many 

 portions of Madagascar, and that in few places could that 

 agency have been present on a grander scale than in the great 

 volcanic region of which Madagascar is the centre, and the 

 Comoro and Mascarene groups the extreme points in either 

 direction. 



An attempt has been made in the accompanying sketch- 

 map to show the prominent features in the physical geography 

 of the island already noted. Probably closer examination 

 would show that the detached groups of extinct craters are ' 

 all connected by intermediate links, so as to form a continuous 



