318 THE DESERT SANDSTONE. 



to resemble a flock of sheep feeding on a snow covered plain. The 

 ash was grey, but where exposed to the bleaching effect of the 

 sun's rays, had become white. The composition of the ash was 

 according to Prof. Liversidge, as follows : — 





I. 



II. 



III. 



Loss on ignition 



2-17 



2-74 



212 



Silica ... 



63-30 



65-04 



68-06 



Alumina 



14-52 



14-63 



15-03 



Iron sesquioxide 



" ] 5-82 



( 4-47 



•28 



Iron monoxide 



I 2-82 



3-66 



Manganese 



•23 



trace 



trace 



Lime 



4-00 



3-34 



2-71 



Magnesia 



1-66 



1-20 



•81 



Soda 



5-14 



4-23 



4-25 



Potash ... 



1-43 



•97 



3-41 



Titanic acid ... 



1-08 





•38 





99-35 



99-44 



100-71 



No. I. by Sauer, No. II. by Eenard, No. III. by K. Oebbeke. Journ. 

 ■Chem. Soc, 1884, p. 974. 



Professor Judd dealing with the nature of the materials ejected 

 points out that the compact lavas poured forth from Krakatoa at 

 the close of the eruption, contained as much as 70 per cent, of 

 silica, the dust derived from which of course would be nearly a 

 pure sand. The lavas were porphyritic pitchstone and obsidian. 

 The heavier lava dust, which fell in Java, and was examined by 

 numerous geologists contained almost every variety of felspar- 

 crystals.* The minute ejecta, consisting of pumice as well as finer 

 dust, carried by the unusual violence of the explosions into the 

 higher atmospheric regions, where it remained suspended for very 

 long periods, was thus drifted to enormous distances from the scene 

 of the eruption, showing how volcanic material even from one point 

 of ejection may be spread over immense areas. The whole of 

 this material from the rapid rate at which it cooled, was a volcanic 

 glass of high specific gravity and slight friability. The most 

 characteristic substance in these dusts was rhombic pyroxene or 

 augite. f 



The above analyses show ash derived from a lava of the 

 intermediate character and such deposits are usually grey when 



* Professor Judd considers this to be without precedent amongst 

 volcanic products. See Report of the Krakatoa Committee of the Royal 

 Society, London, 1888. 



f As an instance of the extent and distance to which this augitic dust 

 was carried I may mention that when making a series of soundings 

 between the Philippines and Moluccas in 1886, there was always an 

 admixture of fresh pyroxene crystals amongst nearly every specimen 

 of the sea bottom. On the north coast of Australia it was especially 

 •abundant. 



