RECENT VOLCANOES. 277 



They belong to a late period of the history of the volcano as is shown 

 by their stratigraphical position and by the great amount of denuda- 

 tion undergone by the underlying ash-beds previously to their appear- 

 ance. On the other hand, there exist also some older lava-flows in- 

 terbedded with the ash-beds and agglomerates t There are also some 

 lavas which seem newer still than those of the great inclined plateaus, 

 and are probably the latest products of activity. They occur at 

 the junction of the second cone with the eastern one and are shown 

 on the map with a purple colour. They are more basic than most 

 of the other rocks. They show a distinctly columnar structure 

 and occur at very variable altitudes, frequently occupying the 

 bottom of valleys, so that when they were ejected the topography 

 was already not unlike what it is to-day. 



The fragmentary beds which form the most considerable portion 



of the volcanic deposits are of various degrees 

 Ash-beds, tuffs, etc. & 



of coarseness, from the finest ash up to masses 



consisting of boulders as much as one foot in diameter. All these 

 fragments are irregular and angular. There are also found occa- 

 sionally some real "bombs" which were ejected in a molten or 

 pasty condition and which have a chilled outer crust (specimen ^ 6 3 T ) , 

 The desintegration of these ash-beds has produced a gigantic talus 

 forming a deeply ravined slope all round the mountain. The materials 

 of all sizes have been reconsolidated into beds which so resemble 

 the ash-beds from which they were originally derived that it is often 

 difficult to tell whether it is the result of former eruptions or of later 

 desintegration, a distinction rendered still more difficult owing to the 

 fact that denudation was proceeding simultaneously with the later 

 eruptions. 



The fragments that constitute the agglomerates and ash-beds 

 consist of andesitic lavas of the same class as those that form the lava- 

 flows. When unaltered they exhibit the same grey colour, but usually 

 they have undergone a certain amount of chemical alteration, probably 

 of a solfataric nature, which has coloured them in exquisite shades or 

 salmon pink, buff, green, mauve, and many other tints. These 

 H 2 ( 99 ) 



