220 THE VOLCANIC DISCHARGE 



long steep western ridge or crater wall, and the deep chasm 

 sweeping down from it. 



It may just be said further, that the slopes of the crater both 

 inside and out are covered with turf, which grows on a dark 

 brown volcanic soil, mingled with rounded pebbles of greenish 

 or purple lava, very compact and close in structure, and con- 

 taining minute crystals scattered sparingly through it. Occa- 

 sional blocks of this are found round the edge of the crater 

 wall, and the same rock crops out at many places on the steep 

 inner slopes. I did not notice any vesicular lava or scoria ; 

 and at a little homestead not far from the north-eastern foot of 

 Tritriva, I was surprised to find the hcidy or fosse dug to twelve 

 or fourteen feet deep almost entirely through the red clay or 

 earth found all through the central regions of the island. The 

 dark brown volcanic soil, here seen in section, appeared to be 

 only eighteen inches deep, with layers of small pebbles. So 

 that the discharge of the volcanic dust and ash appears to have 

 extended only a short distance from the mountain ; at least it 

 does not appear to have been very deep, unless, indeed, there 

 has been much denudation. It must be remembered, how- 

 ever, that this point is to the windward side of the hill ; prob- 

 ably the volcanic soil is deeper to the west of it. The much 

 greater height of the western wall of the crater is no doubt 

 due to the prevailing easterly winds carrying the bulk of the 

 ejected matter to the west, and piling it up to two or three 

 times the height of the eastern side. After seeing the amount 

 of gneiss rock which must have been blown out of the vent, I 

 expected to have found much greater quantities of it, and in 

 larger blocks, than the very few and small fragments actually 

 seen on the outer slopes. The greater portion, however, is 

 probably covered up under the quantities of volcanic dust and 

 lapilli which were subsequently ejected. 



Tritriva, it will be evident from this slight sketch, will 

 greatly interest those who have a taste for geology and physical 

 geography ; while its peculiar and somewhat awe-striking 

 beauty makes it equally worthy of a visit from the artist and 

 the lover of the picturesque. Certainly it became photographed 

 upon our memory with a distinctness which rendered it a vivid 

 mental picture for many a day afterwards. 



Returning northward from Antsirabe towards the neigh- 



