CONSTITUTION AND ORIGIN OF SPHERULITES. 429 
When branching trichites are first attacked they disinte¬ 
grate, the particles are hydrated and become brown, but the 
radial arrangement is still very clear. If solvents carry off 
a larg® part of the hydrous oxide, the place of the original 
trichite is often indicated by most delicate, faintly brownish 
lines. The hydration sometimes produces a flocculent mat¬ 
ter which materially obscures the feldspar needles. Each of 
these secondary conditions of the iron oxide corresponds ex¬ 
actly to what has at times been described as the essential 
characteristic of certain spherulites. The various secondary 
forms of iron oxide have even been the only constituents de¬ 
scribed in a spherulite said to show a distinct black cross in 
polarized light. 
The brownish color of the amorphous base between feld¬ 
spar needles is sometimes not referable to individualized par¬ 
ticles ; but if tridymite or quartz crystallizes out of that base 
the iron oxide is excluded and forms distinct particles. This 
brownish color is often mentioned as a property of petrosilex, 
and it is noteworthy that Michel-Levy and Lacroix retain 
this feature in their late definition, cited above, which makes 
spherulitic quartz and feldspar the components of the sub¬ 
stance. 
There are various other features of the mineral constitu¬ 
tion of spherulites well illustrated in the material which has 
been studied, but only those of greatest importance can be 
discussed in the limits of this article. 
Origin of Spherulites. 
It is the writer’s desire to discuss, briefly and in a prelimi¬ 
nary way, the bearing of some of the observations made 
upon the question as to the origin of spherulites produced 
during the consolidation of a rock magma, the agencies in¬ 
volved and the conditions directing their activity to the end 
specified. At present it seems impossible to harmonize all 
the known facts with any theory suggested, but this is doubt¬ 
less because some one of the important agents is unknown or 
