364 Tlie Amaican Geologist. June, i899 
(c) Le Chatelier has shown that CaCOi does not dissociate 
at a temperature of 1,000° centigrade. If it be subjected to a 
pressure of i.ooo kgr. per square centimetre it fuses and on 
cooHng- gives a crystalHne marble. Therefore when the hquid 
magma with CaCOs is under high pressure, there is no disso- 
ciation; there may result calcite, marble, cancrinite. But if 
suddenly the magma communicates with the surface of the 
earth's crust through a fissure, the pressure diminishes, the 
magma differentiates. The presence of water in the glass of 
volcanoes can thus be explained by pressure. Lewinson-Less- 
ing fused pyroxenes, amphiboles and feldspars in an atmo- 
sphere of the vapor of water. The fused magma absorbed one 
per cent, of the w-ater. 
Certain minerals cannot be fused without decomposition. 
If gaseous products are formed during decomposition,- this will 
be stopped by pressure. The author fused hornblende; one of 
the products of the decomposition was olivine. There are also 
gaseous products. Thus the author supposes that olivine 
forms at the expense of the hornblende, but there was none of 
it when the decomposition of the hornblende was prevented by 
pressure. 
(d) Beckstrom states that liquation of liquids is a function 
not only of temperature but also of pressure. Pressure retards 
or prevents liquation when the latter is accompanied by in- 
crease of volume. In the depths of the earth liquation takes 
place slowly, and depends simply upon the temperature; when 
the pressure is lessened liquation takes place more rapidly. If 
the laws of the liquation of mixtures are applicable to magmas 
we shall be able to explain by it the phenomena of "composite 
dikes", etc., but these phenomena are but little studied. The 
author supposes that liquation explains the formation of the 
large crystals of feldspar, in the andesytes, filled with inclusions 
of glass. The liquid, or rather the viscous, magma already 
feldspathized is mixed with another magma. When, for ex- 
ample, pressure diminishes rapidly, the feldspar, which has 
been a longtime viscous, crystallizes rapidly, and imprisons 
within itself the other magma forming drops in the crystal. For 
units of surface of the crystal there should be, according to 
the author, an equal number of inclusions, if this reasoning is 
correct. 
