106 



Messrs. D. Herman and F. Rutley. 



The little nebulous patches are mostly circular in form, and these 

 circular patches often coalesce. There are a few instances in which 

 the globulites occur within sharply defined circular or approximately 

 circular boundaries, but for the most part the nebulous patches shade 

 gradually away into the glass. One of these patches magnified 

 820 diameters is shown in fig. 12, Plate 3. The structure fore- 

 shadowed in this and in Specimen 126, may be regarded as 

 spherulitic.* 



Specimen No. 147 is especially interesting on account of the per- 

 fect manner in which it demonstrates that devitrification takes place 

 from the surfaces of a crack, just as from any other surfaces. The 



* A very interesting example of a like structure, but on a much larger scale, is 

 seen in a specimen of obsidian collected by Mr. John Arthur Phillips, at Hot 

 Springs, near Little Lake, in California. The obsidian is black and contains several 

 greyish- white, or yellowish-white, spheroidal bodies (lithophysen of Richthofen), 

 which range up to an inch in diameter. These, when examined carefully, are seen 

 to consist of numbers of small spherules, about ^ of an inch in diameter, but many 

 of still smaller dimensions. The minute spherulitic structure of these large spherules 

 i9 best seen on weathered surfaces, but even on fractured surfaces the spherules may 

 still be seen, though their spherical character is less clearly visible, owing to inter- 

 stitial matter, which becomes removed by weathering. In these larger spherules 

 there is evidence, though obscure, of a radiating structure. The mimicry of the 

 little spherules built of globulites, in Specimens 126 and 127, by these large 

 spherules built of little spherules, in the obsidian, is very striking, but it is quite 

 probable in the latter case that the smaller spherulitic structure was set up in the 

 large spherule after its formation, the vestiges of a radiating crystalline structure 

 tending to confirm this view. 



Fig. 4. 



Part of large spherule in obsidian from Hot Springs, near Little Lake, California. 



