CONSTITUTION AND ORIGIN OF SPHERULITES. 433 
spathic growth in the spherulites studied by the writer seems 
inseparable from that regarding the meaning of the concen¬ 
tric structure and the regularity of the outer form. In con¬ 
sidering these problems we must take into account all avail¬ 
able data as to the condition of the magma at the time of the 
spherulitic formation. We know that the lava had come to 
rest, for the fluidal structure caused by the movement of the 
magma during eruption traverses the spherulites undis¬ 
turbed as to course. The mass must have been nearly solid, 
yet capable of being locally softened or rendered viscous 
again, by the agencies involved in the formation of spheru¬ 
lites. The heat liberated during rapid crystallization and 
the influence of superheated water and steam are factors 
which were doubtless potent in producing this result. A 
very remarkable occurrence at Silver Cliff is full of signifi¬ 
cance in this connection, though its full meaning is not yet 
clear. 
In some of the enormous compound spherulites of the type 
represented by figure 1, Plate 6, there is a very marked 
breccia structure. The fragments are sharply angular, of 
various sizes up to two or three inches in diameter, and are 
defined as fragments by the dislocation of the fluidal struc¬ 
ture, and by a slight brownish color in the more finely 
brecciated parts. The first idea is that the spherulite has 
been fractured, but the outer surface shows no dislocation of 
parts, and closer examination proves that both generations of 
spherulitic growth traverse these fragments without change in 
course. The symmetry of the spherulite is not affected by the 
interior breccia structure, which is thus clearly of older date. 
The same breccia structure is, however, found locally in the 
perfectly fresh pitch stone of the same flow. Here the frag¬ 
ments seem almost welded together, so perfect is the union 
of surfaces on which a sharp dislocation of the fluidal struc¬ 
ture takes place. It appears that the lava must have been 
in a very stiff viscous state, just prior to final consolidation, 
when by some sudden and violent volcanic shocks it was 
broken into pieces, which still possessed plasticity enough to 
perfectly coalesce again under the pressure upon them. 
