BY VV. G. WOOLNOUGII. 523 



The gas-cavities call for no special remark. They resemble 

 the glass-inclusions in size and shape. 



The individualised inclusions can be referred to augite and 

 magnetite. In all cases the former is yellowish-green in colour, 

 with perfectly normal refractive index and double refraction. It 

 occurs in two distinct habits: (i.) rounded or irregular grains 

 generally more or less centrally arranged, and (ii.) prisms exactly 

 similar to those in the base arranged peripherally and generally 

 parallel to crystal edges. The grains are mostly about 0-02 mm. 

 diameter or smaller, though occasional fragments up to 0*2 mm. in 

 length may be observed. 



Magnetite grains are far less abundant than augite, and are 

 usually about 0-02 mm. diameter. They are as a rule strongly 

 idiomorphic. 



The "dusty'' inclusions have the form of minute lines and dots 

 which are certainly connected with the phenomena of corrosion 

 and rejuvenescence. 



These latter effects are very strongly marked, some crystals 

 having been almost entirely redissolved by the magma. Such 

 sections exhibit what have been termed above "dusty" inclusions 

 in enormous numbers round the periphery. They are connected 

 with the magma in many cases, and form a sort of frayed out 

 fringe of it extending towards the centre of the crystal. They 

 are reall}^ solution cavities, and are so abundant in some sections 

 that the original crystal has been con^'erted into a veritable 

 sponge. Sometimes they extend to the very centre of the crystals, 

 in other cases a nucleus of clear, uncorroded felspar is left, while 

 again they have travelled along several lines leaving clear portions 

 between. This corrosion is by no means universal; in fact the 

 bulk of the sections show little or none of it. I am unable to 

 account for this selective effect, as there does not appear to be 

 any notable difference in the composition between those affected 

 and those left. It may be that the freedom of most sections may 

 be apparent and not real. The solution may have affected onlj^ 

 a very narrow zone, so that, when the section passes through the 

 plane of corrosion, the felspar appears crowded with "dusty" 



