136 



THE VOYAGE OF H.M.S. CHALLENGER. 



the normal phonolites already described, except, perhaps, that the sections of sanidine 

 are somewhat larger. 



Another hill situated at this part of Greenland Harbour is formed of a trachytic 

 rock. It is a rounded eminence crowned by a mass of angular blocks, scattered about 

 like the ruins of masonry. The rocks collected here by Mr. Buchanan are augitic 

 trachytes, identically similar to those already described ; they were obtained from the 

 bed of a river entering Eoyal Sound. The rocks are compact, with a slightly greasy 

 lustre, and a subconchoidal fracture. They are bluish grey in colour, sometimes with 

 macroscopic sections of sanidine, sometimes marked with circular black spots, either 

 extended in a zone or combined to form more or less continuous bands. The 

 microscope shows broken crystals of sanidine and microliths of augite grouped round 

 hornblende sections, only traces of which now remain. These augitic microliths 

 combined with grains of magnetite tend to replace the amphibolic mineral, and in some 

 cases do so completely. The sections of these minerals are embedded in a ground-mass 

 formed principally of small lamellse of sanidine. A specimen of these trachytic rocks 

 from Greenland Harbour has been analysed by Dr. Klement with the following result: — 



I. ri738 grammes of substance, dried at 110°C. and fused with carbonates of 

 potassium and sodium, gave - 0188 gramme of water, - 6835 of silica, 0"2453 of 

 alumina, 0"0065 of ferric oxide, - 0380 of lime, 0'0126 of magnesium pyrophosphate 

 and traces of manganese. 



II. 0'9893 gramme of substance, treated with hydrofluoric acid, gave - 2069 

 gramme of chlorides of sodium and potassium, yielding 0'2998 of potassium 

 chloroplatinate. 



III. l - 0507 grammes of substance, treated in a sealed tube with hydrofluoric and 

 sulphuric acids, was titrated with potassium permanganate and 3 '4 c.c. of solution were 

 required to oxidise the ferrous oxide (1 c.c. = 0'005405 gramme FeO). 



Percentage Composition. 



101-36 



This analysis corresponds closely with the average composition of trachytes. The 



