160 THE AMERICAN NATURALIST. [VoL. XXXIV. 
PETROGRAPHY. 
Experimental Petrography. — With the increasing number of 
experiments being made in the attempt to discover the laws govern- 
ing the formation of crystalline rocks from their magmas some 
important truths should soon be disclosed. The latest contribution 
to the subject has recently been made by Bauer,! who worked along 
conventional lines. He fused powdered rocks, mixtures of powdered 
minerals, and mixtures of chemical compounds, with and without the 
addition of *mineralizers," held them at temperatures of 1000°—1400° 
for ten or more hours, and then allowed them to cool. Unfortu- 
nately he was unable to prolong the cooling stage to any great extent, 
and consequently the products obtained were largely glassy. 
The wolframates, boric acid, and borax served well as “crystal- 
lizers." Under the influence of the first, quartz was produced, and 
with the aid of the other two, hornblende. The addition of the 
chlorides and fluorides to the mixture appeared to serve simply to 
lower the fusing point. 
The quartz was obtained as irregular grains in a mass composed 
of a groundmass of glass, enclosing small laths of feldspar and larger 
crystals of orthoclase, albite, olivine, and nepheline. This was pro- 
duced by fusing a mixture of orthoclase, albite, mica, hornblende, 
sodium chloride, potassium tungstate, boric acid, and sodium phos- 
phate. The quartz is thought to have originated in the breaking up 
The hornblende was obtained in three experiments. The most 
interesting consisted in the fusion of a mixture of powdered phono- 
lite and nepheline-basalt, neither of which contained any trace of the 
mineral. The hornblende was a bright-green variety. In one of 
the other two experiments powdered diorite was fused with boric 
acid, sodium phosphate, and calcium fluoride at a temperature of 
1000°. The resulting hornblende was brown, while that in the origi- 
nal diorite was green. 
The third experiment yielded also brown hornblende. In this 
powdered hornblende was fused with sodium and calcium fluorides 
and magnesium chloride. 
Another interesting result reached was the discovery that the same 
mixture under different conditions of temperature and rates of cool- 
ing may yield entirely different products. For instance, the powder 
1 Bauer, K. Neues Jahrb. f. Min., etc., Bd. xii, p. 535. 
