134 Transactions. 



the microscope the groundmass is seen to consist of complete 

 spherules and sectors of spherules, with the interstices between 

 their peripheral boundaries filled in with micropegmatite and a 

 quartz mosaic. Approximately the area covered by the spheru- 

 litic growths is about two-thirds that of the total groundmass. 

 Some of the individual spherules attain a diameter of 3 mm. 

 The peripheral boundaries of the best-developed spherules are 

 not perfect circles. The final consolidation of the rock appears 

 to have taken place before the development of the spherules 

 was completed. In parts the spherules have impinged upon 

 one another, and the boundaries of the two individuals are 

 coterminous. Where this happened further development could 

 not go on, and this seems also to have been the case where the 

 space between the two individuals is filled with a fine granular 

 mosaic of quartz. Here the growth of the spherule ceased when 

 no more feldspar matter was available ; but where the inter- 

 vening space is filled with a micropegmatitic intergrowth the 

 spherule has continued to advance, and at the final consolida- 

 tion a portion of the micropegmatite arranged itself in delicate 

 fern-like outgrowths around and continuous with the spherule. 

 A radial growth corresponding to sectors of a spherule occur 

 around the phenocrysts, and extend some distance into the 

 groundmass. The spherules are composed of a pegmatitic 

 intergroAvth of quartz and orthoclase varying in texture from 

 cryptopegmatitic* near the centre to micropegmatitic near the 

 circumference. Arranged radially to the centre, and some- 

 times extending nearly the complete radius of the spherule, are 

 needles, long blade-like crystals and peg-shaped inclusions of 

 riebeckite. This mineral is present in larger crystals, with 

 ragged outlines and no definite shape in the groundmass, between 

 the spherules ; and in many portions of the slices the larger 

 crystals occur with their longer axis tangentially arranged 

 around the outer edge of a spherule. Riebeckite also occurs 

 as minute inclusions in the quartz and perthite phenocrysts. 

 By transmitted light the colour of the mineral is indigo blue, 

 and the pleochroism — (a) black, (b) dark-blue, (c) brownish- 

 yellow — appears to correspond most nearly with that of the 

 riebeckite described by Le Verrier from Corsica ; it also re- 

 sembles that from Dongo Hiiro, described by Prior. The needle- 

 like blades in the spherules attain a, length of 1 mm. The 

 phenocrysts are quartz and perthite. Some of the quartz 

 crystals have sharp outlines and angles ; in others the angles 

 are rounded by corrosion. The quartz is relatively free from 



* Perhaps this term is not strictly correct, as the -tructurc can be 

 resolved under a magnification of 4oo diameters. 



