432 
CROSS. 
result. If this forking is continued arborescent growths are 
produced. While the physics of these curving growths are 
as yet imperfectly understood, it seems that a certain degree 
of viscosity of the medium in which the crystallization pro¬ 
ceeds and a great rapidity in the process are essential factors. 
Lehmann expresses the belief that most substances crystal¬ 
lizing out of solutions can be made to form branching 
growths under proper conditions. 
Applying this idea to crystallizations met with in glassy 
lavas, we’ find that certain forms are almost completely 
analogous to some that have been observed in synthetic ex¬ 
periments, as, for instance, the curling or knotted bunches 
of trichites, forked microlites, and the beautiful feathery 
shapes assumed by augite in the pitchstone of Arran, or in 
the basalt of the Sandwich Islands described by E. S. Dana.* 
But these crystallizations are not complete spherulites; they 
are simply branching crystals, and correspond to but one 
element in a spherulite of the type under discussion. In no 
spherulite examined by the writer can all of the branching 
feldspars be assumed to spring from a single original crys¬ 
tal. They start from many such centers, so that the feld- 
spathic part of each spherulite is a complex of many arbo¬ 
rescent individuals. A single branching individual that 
acquires a spherical form by curving about until the primary 
crystal grain is in the center of the body is called a “ Sphse- 
rokrystall ” by Lehmann, who compares such a growth with 
the spherulite thus designated by Rosenbusch. But the ra¬ 
diate aggregate consisting of a single mineral to which 
Rosenbusch gives the name can seldom, if ever, be an indi¬ 
vidual such as the Sphserokrystall of Lehmann. The criti¬ 
cism of Cohenf that a radiate aggregate of crystals should 
not be called a Sphserokrystall will undoubtedly hold good 
for nearly all cases coming under Rosenbusch’s definition. 
The question as to what has caused the branching feld- 
* Contributions to the petrography of the Sandwich Islands. Amer. 
Journ. of Science. 8°. New Haven, 1889, June, vol. 37, pp. 441-467. 
f Gottingsche gelehrten Anzeigen, 1886, p. 915. 
