428 OK COMPOSITE SPHEKULITES IxV OBSIDIAN EEOM CALIFORNIA. 



by tlie radial fibrous structure of the large spberulile with which 

 they are incorporated. 

 Fig. 2. Ditto, X 195. Ordinary transmitted light. 



The radial structure is here seen to be crossed by short and delicate 

 ci)-cumferential shrinkage cracks. The crystals and specks are 

 magnetite. 



3. Part of the same spherulite, X 45. Ordinary transmitted light, showing 



concentric banding. 



4. The same part of the section shown in fig. 3, X 45, dark-ground 



illmuination. By this method of illumination the composite nature 

 of t lie spherulite becomes clearly demonstrable, and it may be shown 

 that it is composed of a number of small, closely packed, primitive 

 splierulitee, thi-ough which the concentric banding is seen to pass. 



5. Eadial fibrous stnature of the same spherulite, as seen between crossed 



jiicols, the principal sections of the latter being situated at 45° to 

 the general direction of the fibration. The fibres are felspars, appar- 

 ently orthoclase, X 195. 



6. Marginal portion of the same spherulite, showing smaller outlying 



spherulites, around which an independent radial crystallization has 

 been set up, X 18. Oblique ordinary transmitted light. 



Discussion. 



The Chairman said that the sequence of the different portions 

 brought forward with so much care by the Author is one which 

 admits of much discussion. 



Rev. E. Hill said that the explanation of the divergence of these 

 crystallizations was extremely interesting. As to Avhich structure 

 came first, it is difficult to determine. In the section exhibited 

 under the microscope he agreed with Mr. Rutley as to the se(juence. 

 The question of molecular motion after consolidation in igneous 

 rocks is a subject of great importance. 



