BY W. G. WOOLNOUGH. 519 



dant in, but by no means confined to. certain very much corroded 

 crystals, and in these cases pass insensibly into the hair-like 

 microUtes in the base. Their exact nature is somewhat doubtful. 

 They are certainly not hornblende (too high an extinction angle), 

 but are more likely augite. They are, however, distinct from the 

 perfectly definite augite microlites (No. 1 above). The two kinds 

 occur in the same felspar crystal. 



(3). Magnetite grains surrounded by radial and, in some cases 

 concentric contraction cracks, are only sparsely distributed. 



The most numerous inclusions are unindividualised. These 

 consist of glass which in the smaller occurrences is colourless, but 

 in the larger ones takes on the character of the base, that is, 

 becomes brown in colour, and crowded with microlites. The 

 small colourless ones are more or less rectangular in outline, and 

 are of the nature of negative crystals (fig. 5). In almost every case 

 these small inclusions contain a relatively fairb/ large fixed 

 bubble, and are strikingly like those figured by Cohen. ^ The 

 markedly brown inclusions are for the most part irregular in 

 shape, and are probably more of the nature of solution cavities 

 rather than true inclusions. In one or two of the most corroded 

 crystals, distinct necks can be found joining them to the substance 

 of the base. In those crystals which have been added to second- 

 arily, the inclusions cease abruptly at the original somewhat 

 rounded surface, and the more acid peripheral zone is quite free 

 from them. The explanation of the arrangement of the inclusions 

 is probably that the original basic felspars suffered very consider- 

 ably from corrosion by the magma. The solution followed the 

 plane of the (010) cleavage mainly. Afterwards, through change 

 of conditions another period of felspar-building followed, and the 

 outer inclusion free zone of acid felspar was added. 



* Sammkang von Mickrophotographien zur Verauschaulichung der mikro- 

 skopischen Structur von Mineralien und Gesteinen. Taf, viii., ix., x. 



