222 REV. J. MILNE CURRAN. 



the unaided eye, a fine glistening structure is the only indication 

 of its varied constituents. A hand-lens will show an occasional 

 porphyritic mineral not more than half a millimetre long. On 

 slicing the rock these prove to be olivines or augites. It decomposes 

 to a light grey crust as seen in the specimens exhibited. This by 

 the further removal of its more soluble constituents becomes the 

 soapy stiff rock in appearance, not unlike fuller's earth, that fills 

 the fissures already referred to. The light grey colour of the 

 decomposed crust is somewhat remarkable, as the rock contains 

 13% of ferrous and ferric oxide — quite as high a percentage as 

 many basalts have that weather to a bright red clay. A polished 

 slab of the rock is etche d with more than ordinary rapidly by 

 hydrochloric acid. The polished slab is almost black. When 

 acted on by the acid it shows a light grey ground with the un- 

 attacked minerals standing out as black granules. Its specific 

 gravity is 2-94, a density somewhat above typical basalt. 



Magnetic Properties. 

 The appearance of the etched surface suggested trying the effect 

 of a magnet on the rock. A thin bar of the basalt, five milli- 

 metres long was cut, and I found that a magnet lifted the bar 

 readily. A second bar was cut and mounted as a magnetic needle. 

 Permanent polarity was induced in this by placing it between 

 the poles of an electro-magnet, with the result that the needle of 

 rock became sensitive to opposite poles of a magnet. It is too 

 heavy to respond to the directive influence of the earth's mag- 

 netism, but on subjecting the whole apparatus to a gentle vibratory 

 motion the bar will set north and south. 



Chemical Composition. 

 The peculiar colour of the weathered basalt that was immediately 

 around the fresh rock, suggested the determination of its solubility 

 in acids ; *5 gram of finely powdered basalt was digested in dilute 

 hydrochloric acid for two and a-half hours, then it was heated 

 with strong acid for one and a-half hours, with the result that 

 •218 gram remained insoluble. This gives 56-4 per cent, of the 

 rock as soluble in hydrochloric acid. 





