56 BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



kittet sind. Die Diabasbrockchen, welche sichtlich durch abroUung ihre abge- 

 rundete Form erhalten haben, sind meist stark zersetzt, lassen jedoch noch 

 deutlich die Texturverhaltnisse des Krystallinisch kornigen Gesteins in der 

 Verschiedenartigkeit des Diabases wahrnehmen. * * * Dazu gesellen sich 

 zuweilen Brocken oder knollenartig rundliche Stiickchen mehr oder weniger 

 veranderten Nebengesteins, namentlich Fornfelsahnliche Fragmente und kugelige 

 Ausscheidungen, welche beim Durchschlagen die Ziisainmensetzung der als 

 Perldiabas beschrieben Varietaten besitzen. Diese enthalten haufig im Centrum 

 grossere Putzen von verandertem Gestein, um welche sich mit nach aussen 

 abnehmender Haufigkeit einzelne kleine Perlen oder Knollchen der veranderten 

 Substanz in zonen- oder schalenahnlicher Anordnung anlegen. (Berneck.) 



The spherulites of the acid volcanic glasses like those of the Yellow- 

 stone National Park, in appearance and mode of occurrence often so 

 closely simulate the kugels of meteorites as to demand attention here. 

 Indeed Klein ^^ affirms that those kugels with radiate structure : 

 "Echte spharolithe darstellen." Berwerth, too, it may be recalled 

 compared the kugels in meteorites to the spherules in artificial 

 glasses, an error to which I have elsewhere called attention. ^^ 



The term spherulite, as now used by the leading petrologists, it 

 may be said, refers to the complex growths of minerals of one or more 

 species, principally miscroscopic quartz and orthoclase with minor 

 quantities of tridymite, colloidal silica, and minute forms of other 

 accessories characteristic of highly siliceous igneous rocks. "The 

 essential character of spherulitic growth is the crystallization of 

 minerals from one or more points with a radiating or divergent ar- 

 rangement." (Iddings.) In external form they are often beauti- 

 fully spheroidal, though not necessarily so, and break from the matrix, 

 with which they are practically identical in composition, as freely as 

 do the chondrules from a meteorite of the spherulitic chondrite type. 

 In thin sections between crossed nicols they show a black cross which 

 is due to the elongated form and radial arrangement of the principal 

 constituents. That they originate in place and their formation is 

 but a peculiar phase of magmatic crystallization is unmistakable. 

 The question of their origin throws no light upon that of the granular 

 and porphyritic chondrules, and seemingly none upon those of the 

 eccentric radiating type. 



Brief reference should be made to other occurrences of kugellike 

 forms in terrestrial rocks. 



The kugels of the spheroidal granites of Donigal, England, West- 

 moreland, Sweden, Quonochontogue Beach, R. I., and those of 

 Finland, recently described by Sederholm ^^ all show a marked con- 

 centric structure, rarely if at all simulated by the meteoric chondrule. 

 The nearest approach to these forms that has thus far come under 



«8 Studien iiber Meteoriten, 1906, p. 35. 



18 Bull. Geol. Soc. Amer., vol. 32, 1921, p. 409. 



20 Bull. Com. Qeologique de Finland, No. 83, 1928. 



