CONSTITUTION AND ORIGIN OF SPHERULITES. 435 
such a surface on a specimen from a large spherulite. A 
portion of the vein against which this undulating surface 
was developed is shown resting on it, in the left central area 
of the figure. The fractured surface of the lower part of the 
specimen shows the delicate development of the early growth, 
here subordinate to the latter one. It is evident that the 
vein-like space whose walls are thus moulded cannot be 
thought of as a fissure cutting into solid rock. An explana¬ 
tion is suggested below. 
Further evidence that the agencies active during the 
periods of spherulitic growth were able to soften or even 
liquefy the viscous mass is found in many places. In cer¬ 
tain rocks of the Rosita Hills where there are three or four 
generations of spherulites the residual growth is character¬ 
ized by large curving trichites, which form a heavy fringe 
about the earlier crystallizations, and in other cases large 
knots of trichites have developed in the residual space, 
exactly like those of some obsidians and quite unlike the 
earlier trichites of this magma. In such cases the original 
fluidal structure of the magma is seen traversing the earlier 
spherulites up to the boundaries of the residual space, but cut 
sharply off on that line, the augite and feldspar microlites 
and the small primary trichites having been completely 
resorbed, while a fluidal structure pertaining to the residual 
period has resulted from minor movements which drew out 
and deformed the new trichitic knots in the narrower spaces 
between the spherulites. Residual spherulites develop in a 
part of the area characterized by these trichitic knots. 
In order to explain the phenomena above described the 
writer wishes to advance an hypothesis as to the conditions 
favorable to or causing spherulitic growth in the cases which 
have been specially considered. It is an attempt to explain 
the close and seemingly interdependent relationships exist¬ 
ing between the outer form, the concentric zones of growth, 
and the branching character of the feldspathic contituent. 
The fact that such spherulites are especially characteristic of 
lavas rich in silica and containing some water, together with 
56—Bull. Phil. Soc., Wash., Vol. 11. 
