378 The American Geologist. June, i890 
Obsidians, especially, furnish us Avith the most interesting ob- 
jects for studying the economy of crystal life, as they reveal 
an almost endless variety of intermediary forms. Some are 
perfect natural glasses, free from every trace of devitrification : 
here the cooling was too rapid to permit even the formation of 
globulites. In others we have the field crowded with spherical 
bodies of uniform size, evidently globulites which were arrest- 
ed in their further development by the solidification of the 
matrix. A third section shows the globulites arranged in 
lines, a fourth is characterized by the presence of an immense 
number of hair-like rods, in a fifth the rods were evidently on 
the point of uniting into planes of symmetry when the process 
was interrupted, and as we extend our inquiry to specimens 
which solidified more leisurely we find a complete "j)erma- 
ment record" of every step of crystalline activity. 
Globulites and their various combination-products may al- 
so be observed in comparatively coarse-grained Basalts, Dole- 
rites, Porphyrites, etc. and their presence does not always indi- 
cate a vitreous condition of the matrix. It must be remem- 
bered that rocks are usually of very heterogeneous compo- 
sition and that the fusion temperature of one mineral often 
differs considerably from that of another. While Augite, for 
instance, will easily melt before the blowpipe, Orthoclase re- 
quired an enormous temperature, and some minerals are prac- 
tically infusible. When an eruptive mass, a lava, composed 
of, say, six different molten minerals, begins to cool, that min- 
eral which requires the highest temperature in order to melt, 
will be the first to solidify. While it already has developed in- 
to more or less regular crystals, the others are still compelled 
to remain in a liquid or viscous condition, until the tempera- 
ture is sufficiently lowered to permit their consolidation in the 
succession determined by their physical properties. 
Now it may happen that after the individualization of sever- 
al of the constituents of a cooling mass, the temperature sinks 
so rapidly that the remaining ones have no time to crystallize, 
thus we find in thin sections prepared from such rocks, side by 
side with, or between perfectly developed crystals of Feldspar, 
Amphibole or other easily recognizable minerals, vitreous and 
semi-vitreous patches of interstitial matter, crowded with en- 
domorphs. What minerals they represent or what forms they 
would ultimately have assumed, if allowed to develop is in 
