Hyndman and Bonnet/ — Analysis of Sphertilites. 3G9 



These analyses differ considerably from those given above. Here 

 not only the silica is greater in the spherulite, but also the lime and 

 alkalies : this gives a perfectly different relation to that found in the 

 above analyses, as shown by the ratio of the oxides. The large 

 quantity of magnesia may be responsible for the difference. 



II. The Artificial Spherulitic Rock. 



The specimen analyzed had been given to Prof. Bonney by 

 Mr. F. Siemens, of Dresden. It was a bottle glass of a rich 

 resin brown tint (such as is often seen in hock bottles), and 

 the spherulites are of a pale-cream or yellow -ochre colour. 1 

 Under the microscope the glass exhibits only the very palest tinge 

 of brown, and is almost free from microlithic enclosures ; these, as 

 far as they occur, being minute specks, like a dark dust. Crystallites, 

 however, project from the border of the spherulite for a short 

 distance into the glass. The spherulite consists 8 of (a) ferrite in 

 small irregular patches ; (b) an acicular clear mineral, clustered and 

 radiating, forming the mass of the spherulite ; (c) tufts consisting 

 of a few clear acicular crystallites, diverging like a bundle of sticks 

 loosely tied in the middle. With ordinary light the railial structure 

 appears to dominate, zoned by concentric, more opaque bands, but 

 with crossed nicols the tufted structure completely overpowers it in 

 certain clearer-looking bands towards the exterior, and is more or 

 less conspicuous in all the outer part of the spherulite, except for 

 about the last one-thirtieth of an inch, where the radial structure is 

 almost exclusively present. The feathery exterior of the spherulite 

 appears to be formed of microliths grouped fern-leaf fashion ; two 

 sets of crystallites diverging at angles of about 50° from a central 

 stem. The crystallites in the tufts certainly extinguish obliquely, 

 though the angles are not large, perhaps within about 12° of the 

 edge. It is difficult to ascertain the extinction of the radially 

 grouped crystallites, but probably this also is oblique. 



Analyses. 



98-48 99-62 99-48 



1 In making this glass the principal material employed is a granite or granulite. 

 See President's Address, Quart. Journ. Geol. Soc 1885, Proc., pp. 88, 90. 



- The description is written from a new slice, which is thinner than the one used 

 in 1885. 



3 TJt supra— Oi two analyses given of the original granite, the most likely one 

 of the two is chosen. 



4 The iron here is probably too high. 5 Probably contains some lime. 



DECADE IV. VOL. III. — NO. VIII. 24 



