362 The American Geologist. June, \im 
fusion; for u'<it, it lowers the point of fusion (as for 
water). 
Lewinson-Lessing supposes that in the fused magma the 
minerals exist in the state of separated oxides — SiO% Fe^Os, 
AUO3, KjO, etc. When these oxides unite to form silicates the 
pressure which pervades the depths of the earth is favorable to 
the formation of minerals of the ferromagnesian order 
which are formed with a diminution of volume. Therefore at 
great depths under high pressure these are the first minerals to 
be formed. But after extrusion, under ordinary pressure, it is 
fusibility only which governs, and then it is the feldspars that 
crystallize first, and afterwards the ferro-magnesian silicates. 
In the depths of the earth the order of consolidation of the 
silicates should .therefore be in the order of diminution of the 
coefficient T-^t shown in the foregoing table. These considera- 
tions relative to the action of pressure on consolidation and 
volume have been expressed by Brauns in ''Chemical Miner- 
alogy," by Neiss, Sorby, etc. 
As to other factors that influence the order of consolidation 
of minerals, there remain: (i) The affinity of the bases for 
SiO=. (2) The effect of specific gravity. (3) The role of pres- 
sure. 
(1) Affinity of the Bases for SiO.^. 
When two. bases are placed in the presence of an acid, the 
division of the acid between them is not equal, but in propor- 
tion to the affinity between the bases and the acid. If the base 
has a strong affinity for the acid, it often forms acid salts (if 
the acid is polybasic), such as KOH, H2SO4 and KHSO4. 
Potassium has more affinity for SiO^; than the other metals, 
and therefore tends to form salts which are as acid as possible. 
The author allows that SiO^ is divided between the bases al- 
ready in the liquid magma; and that potassium takes posses- 
sion of SiO^ in greater proportion, leaving the other metals to 
share in the remainder. Its action is counterbalanced by the 
affinity of MgO for SiO^ which is also very great. In this re- 
spect the metals succeed each other in the following order: Po- 
tassium, magnesium, sodium, calcium. These ideas have been 
developed by Lemberg in "Ueber Silicatumwandlungen." 
