AGENCIES OF METAMORPHISM 409 



"Kugelbilduugen erscheinen ja auch auf unserer Ercleuberall dort wo natur- 

 liche Oder auch Kiinstliche Glasfliisse einer rasche Abkuhlung ausgesetz sind." 



As a matter of fact, the ^'Kugels'^ of artificial glasses are not chon- 

 drules, but spherulites.^^ 



So far as is known, no systematic attempts at an artificial production 

 of the material under conditions at all satisfactory have as yet been made. 

 Fragments of the Mount Hope, Maryland, gabbro, described by Wil- 

 liams^'' as composed essentially of plagioclase, diallage, and hypersthene, 

 with secondary hornblende, were roasted in a gas blast furnace in the 

 museum laboratory until reduced to molten blebs with cores of still 

 unmelted material. Examination in thin-section showed the pyroxene 

 and amphibolic minerals to have fused to a black glass, while the feldspar 

 (bytownite) was nearly or quite unaltered. A mixture of finely pulver- 

 ized bytownite from Niirodal, Norway, and a light-colored diopside from 

 Siberia yielded a like result. The crudity of these attempts prevents, 

 however, the acceptance of the results as conclusive. 



It is likely that some other agent than heat with or without reducing 

 gases may have been efficacious in bringing about this metamorphism ; 

 and, if this agency were pressure, are there visible proofs of its action? 

 It may be recalled that in my description^^ of the stone from Cullison, 

 Kansas, a hard, compact stone susceptible of a polish, but which, never- 

 theless, I classed as spherulitic chondrite, I referred to an "indistinct 

 wavy banding" visible on a polished surface, which I thought comparable 

 with the "schlieren" structure of terrestrial rocks ; in other words, that it 

 indicated a one-time shearing movement which was, of course, due to 

 pressure (figure 3, plate 5). Little evidence of such a force manifesting 

 itself on the individual minerals and microstructure is available in the 

 literature. That which is here presented is largely the result of my own 

 observations. In many chondritic stones there are well marked instances 

 in M'hich the finer clastic interstitial material seemingly has been formed 

 iDy the more or less complete crushing of the larger forms, productive of 

 what Cohen calls a "pseudotriimmerstructur." Illustrations of this are 

 not rare. 



In the Dhurmsala stone shown in figure 2, plate 5, the large crystal of 

 enstatite near the center has been crowded against the radiate chondrule, 

 fractured, and in places reduced to fragments. Here, as in many other 

 c&ses, however, it is difficult to say just what portion of the fine inter- 



na Pu-sson: Amer. Jour. Sci., vol. 30, 1910, pp. 97-114. 



»T Bull. 28, U. S. Geol. Survey, 1886. 



3s Pi-oc. U. S. Nat. Museum, vol. 44, 1913, p. 327. 



