412 
CROSS. 
Historical Review. 
The term spherulite is one of many in the nomenclature 
of petrography to which no satisfactory and consistent defi¬ 
nition has as yet been given, for the evident reason that 
knowledge concerning the essential character of the objects 
to which the term has been applied is inadequate for the 
establishment of such a definition. A round or spherical 
form is implied by the word, and a radiate or concentric 
inner structure has been found to be a seldom-failing char¬ 
acteristic of the bodies in question; yet, in spite of these 
purely structural conceptions, which are prominent in all 
discussions of the subject, the term has usually been limited 
in its application to masses found in the acid eruptive rocks 
and assumed to be peculiar forms of consolidation of a molten 
magma. 
It is not necessary for present purposes to go far back into 
the literature of petrography, for the views entertained con¬ 
cerning spherulites before the microscope was applied to their 
examination are naturally vague and in a large measure in¬ 
correct. But, although the microscope dispelled certain illu¬ 
sions, it brought out a host of new problems to be explained, 
and in the latest presentations of the subject by acknowl¬ 
edged authorities some important features of spherulites are 
still surrounded by a veil of mystery. 
In 1866 Zirkel states* that spherulites may be considered 
to represent an intermediate stage in the development of the 
crystalline state, between the knotted trichites or crystallites 
of many obsidians and the perfect crystals of the same rock. 
--:- \ - 
* Zirkel (F.). Lehrbuch der Petrographie. 8°. Bonn, 1866, vol. II, p. 253. 
“ Die Spharolithe scheinen eine ahnliche Bildung zu sein, wie die soge- 
nannten Krystalliten in den langsam abgekuhlten Glasern, dem Reaumur- 
schen Porzellan ; sie diirften eine Mittelstufe in der Entwicklung des 
krystallinischen Zustandes darstellen, einerseits zwischen jenen Knotclien, 
welche sich mitunter in den Obsidianen finden, und welche als die un- 
vollkominensten Producte gelten konnen, die eine rasch erkaltende Masse 
in ihrem Bestreben Krystalle auszuseheiden, hervorzubringen vermag, und 
andererseits den vollkommen ausgebildeten Krystallen in der Glasgrund- 
inasse. 
