JoLY — Notes on Volcanic Ash from Krahitoa. 297 



the ash. Remarkable deposits of it, having the appearance of in- 

 filtration along cleavage planes, occur occasionally in feldspar 

 crystals. 



Among the amorphous fragments, Olivine was not observed; 

 many fragments picked up on suspicion being found to be easily 

 soluble in hydrofluoric acid. 



One of the most interesting features of this ash is the nature of 

 the various enclosures in its principal minerals. They obviously 

 give us a means of judging of their relative order of formation. 



Classifying on this basis, Magnetite would come first in order 

 of formation. It occurs as an inclusion in all the silicates present. 

 It will be noticed protruding from the crystals of hypersthene in 

 figures 3 and 4. 



Fyrites might be of contemporary origin. 



The Pyroxenes would in that case be second in order, for while 

 including magnetite they are themselves included in the feldspars. 



The Feldspars were probably the last minerals formed. 



Vitreous inclusions are abundant, generally iron stained to a 

 light-brown, tint and enclosing the bubble which probably started 

 their formation. Yery often these inclusions are ranged parallel to 

 the outline of the crystal ; often again the vitreous mass has iiad 

 the symmetrical form of the containing crystal impressed upon it. 

 Sometimes then by their individual form, sometimes by their dis- 

 position, it is possible to judge of the former crystalline symmetry 

 of a mere formless fragment containing such enclosures. 



ADDITIONAL NOTES. 



Subsequent to the reading of the foregoing, the author received 

 many additional samples, both of the ash and of the block pumice. 

 To the courtesy and kindness of Mr. T. Brewis the author owes these 

 specimens m the first instance. Through information received from 

 that gentleman samples were obtained from Captains who were in 

 the neighboiuiiood of Krakatoa during the period of the eruption. 

 To Captain Ealston, of the Niobe ; Captain Calangich, of the Jafet II. ; 

 and, above all, to Captain Thomson, of the ship Medea, the author's 

 best thanks are due. 



