CONSTITUTION AND ORIGIN OF SPIIERULITES. 41B 
This view is probably based upon the earlier investigations 
of Vogelsang on slags, and upon the resulting theories of crys- 
tallogenesis. Vogelsang himself elaborated this idea in his 
celebrated work, “ Die Krystalliten,” issued in 1875, which 
contained an application of the result of his synthetic ex¬ 
periments to the explanation and classification of spheru- 
lites in rocks. It is not necessary to review the classic ob¬ 
servations of Vogelsang in the field of crystallogenesis, and 
it is no part of the present writer’s purpose to discuss the 
theories of crystal growth which arose from those observa¬ 
tions. He does wish to question their application to a large 
share of spherulitic forms in rocks ; and in this connection 
it may be well to point out that Vogelsang himself seems to 
have appreciated the dangers of this application much more 
clearly than most of his followers have done.* 
The idea that spherulites are not made up of known 
minerals, and that their essential elements are indefinite 
substances, has proven very attractive, both to superficial 
observers and to those whose material would not allow of 
accurate diagnosis. It has therefore been widely adopted, 
and many descriptions of spherulites have been published 
which contain no mention of a definite mineral component, 
although the statements made clearly indicate the presence 
of feldspar or quartz. 
In 1887 Lagoriof speaks of spherulites in terms very 
similar to those used by Zirkel in 1866. 
The views concerning the structure and composition of 
spherulites, found in the petrographical literature of today, 
are naturally the views of the leaders in the respective schools 
* Vogelsang (PI.). Die Krj’-stalliten. 8°. Bonn, 1875 , p. 107 . “Esistnicht 
zu verkennen, dass die Gefahr dabei sehr nahe liegt, zu weit zu gehen, 
und der Idee zu Liebe dem krystallitischen Aggregatzustand ein grosseres 
Feld einzuraumen als er beanspruclien darf;....” 
f “ Ueber die Natur der Glasbasis, sowie der Krystallizationsvorgange im 
eruptiven Magma.” Tschermak (G.). Min. und petrog. Mittheilungen. 
8°. Wien, 1887 ; vol. 8, p. 440 . “Diese letzteren [Spherulites] sind als 
Anfange der Krystallization zu betraehten, die in einem gegebenen Au- 
genblick zum Stillstande kam, sei es, weil das Gestein erstarrte, sei es, weil 
das Magma uberhaupt keine Tendenz besass, die gelosten Silicate auszu- 
scheiden.” 
