THE DESERT SANDSTONE. 317 



oxides, and hence have a higher specific gravity. They are of much 

 darker colour, while fresh lavas of acid composition are usually 

 nearly white. Trachyte, andesite, and phonolite ashes are of 

 various tints of grey. But no ash keeps its colour long : the 

 quantity of iron is too great and the minerals too unstable for the 

 ordinary weathering not to affect them. Moisture soon produces 

 yellow, red, and purple-brown shades. But the mineral character 

 is not lost ; and this mainly consists of silica, no matter what the 

 chemical nature of the ejectamenta is. The acid lavas contain 

 from 60 to 80 per cent, of silica, the basic from 45 to 55, and the 

 intermediate from 55 to 65. Thus silica forms the great mass of 

 the deposit, no matter under what category the lavas are placed. 



I am able to -give an illustration from actual experience of how 

 these sand-beds are deposited. I happened to be on more than 

 one occasion in the neighbourhood of volcanoes during a period of 

 active eruption ; and what I saw in connection with the deposition 

 of ashes helped me much to understand how such formations as 

 the Desert Sandstone have arisen. 



I was in Java about the time of the eruption of Krakatoa, in 

 1883, and visited some portions of the kingdom of Sunda in its 

 neighbourhood. In this case the volcano was in activity from the 

 20th of May casting forth ashes in great quantity. There was a 

 kind of lull again until the 16th of June, when a fresh eruption 

 broke out. Thenceforth there was more Or less a continued 

 scattering of ashes over a wide area. The molten mass below the 

 earth's crust was being acted upon by pressure and gradually 

 approaching the surface upon which the sea-water was producing 

 a violent convulsion. Everybody knows what the result was in 

 the catastrophe of the 27th of August. The whole kingdom of 

 Anjer wherever I visited was covered with a coating of light grey 

 ash, something like snow, a foot deep and more, 130 miles from 

 the volcano. The whole of the intermediate country was covered 

 of course in thicker deposits nearer to the volcano, except where 

 the tidal wave had washed it away. It was incredible what 

 destruction was caused by the ash alone. In one village trees 

 were torn down and great limbs stripped off, as though they had 

 been shrubs. The cocoa-nut trees were mere bare poles. The 

 ash, though apparently so light and insignificant was really very 

 heavy and in a very short time would accumulate in sufficient 

 thickness to bear down even the strong resistance of the stout 

 cocoa-nut palm. Houses were crushed in, roads were obliterated, 

 and the sand silted up in many places so as to cover and conceal 

 fences and hedges. At a tea plantation (Parakansala) where I 

 was on a visit, 100 miles or so to the east of Krakatoa, at about 

 3,000 feet above the level of the sea, the tea plants were curiously 

 covered over with this ash deposit, and the effect at a distance was 



