01 



cross occupies a position analogous to one of the foci of an 

 ellipse. The margins of the spherulites are without the re- 

 markable fringes of the Zeehan variety. An aggregation of 

 minute colourless to brown granules (quartz-orthoclase) fre- 

 quently forms a kind of central nucleus. This centre 

 decomposes, and finally disappears, leaving a foramen. The 

 sectional surface is broken up by radial lines and a reticulate 

 venation marked by iron dust, and the interspaces are orna- 

 mented with a feathery crystallisation of some alumina silicate. 

 The general colour in thin section is grey, stained warm 

 brown by iron. There are some fine examples of double 

 centres and a triple change of crystallisation from centre to 

 circumference. A little quartzo-felspathic ground mass 

 occurs between some of the spherulites containing specks of 

 iron oxide. The specific gravity rauges from 2*62 to 2 64, 

 and in the more ferruginous variety is 2 '66. 



Trial Harbour. — A piece of loose rock which we have 

 examined from this locality is sphernlitic, but has a very 

 different appearance from the preceding ones. Composite 

 spherulites are abundant, and their boundaries are ill- 

 defined. The structure may for the most part be described 

 as of the nature of spherulitic aggregations rather than that 

 of true spherulites. There is a want of symmetry in the 

 arrangement of the component crystals, consequently their 

 axes of elasticity are in different azimuths, and the arms of 

 the cross are disturbed and difficult to locate, "We seem here 

 to have an approach to a pseudo- spherulitic structure, 

 although as the crystalline constituent is only quartz, it may 

 be more strictly correct to describe it as imperfectly spheru- 

 litic. Here and there a little felsitic ground mass is 

 discernible. 



We have an additional sample of a spherulitic rock picked 

 up two miles from Strahan. A noteworthy feature of all 

 these occurrences is that none of them are in situ. The 

 nearest granite appears to be that of Mt. Heemskirk, but 

 whether these several boulders and stones were derived from 

 that particular exposure is, for the present, purely a matter 

 of speculation. 



EXPLANATION OF PLATE. 



Fig. 1. Spherulitic Felsite from Zeehan. 



Figs. 2, 3, 4. Spherulitic Felsite from Castray River. 



Ths figures are photo- micrographs under polarised light and a magnifi- 

 cation of 13 diameters. The dark cros3 is caused by the axes of elasticity 

 in the individual fibres of each spherulite being coincident with their axis 

 of figure. In other words, the arms of the cross represent the directions 

 of the vibration planes of the polarising and analysing prisms. 



