160 
TRANSLATION. 
All Igneous Roclcs derived from two Magmas. —An immense number 
of consequences may be logically derived from the following proposition, 
the proof of which I shall furnish presently, viz. :— That all igneous 
rocks , modern and ancient , were produced by two Magmas , which coexist 
below the solid crust of the globe, and occupy there each a definite position. 
These two Magmas have undergone but slight changes of composi¬ 
tion from the most remote geological epochs; and, moreover, they differ 
essentially from each other by means of well-defined characters. The 
one may, from its excess of silica, be called the Acid Magma; while 
the other is comparable to a basic salt; for its silica is not in sufficient 
quantity to saturate its metallic oxides. The difference of silica in the 
two Magmas is in the proportion of 7:5. They contain nearly the same 
quantity of Alumina ; but the Siliceous Magma contains from one and 
a half to twice as much alkalies, and more Potash than Soda, while the 
reverse occurs in the Basic Magma. The first is specially characterized 
by its poverty in earthy bases, and the iron oxides ; of these, it contains 
from six to eight times less than the other. 
The following Table gives the composition of these Magmas, and the 
specific gravities of the rocks derived from them. 
Table I. 
Proportions 
of 
Elements. 
Silica. 
Alumina. 
Potash. 
Soda. 
Lime. 
Magnesia. 
Oxides oflron 
& Manganese. 
Water, Fluo¬ 
rine, Carbonic 
Acid. 
Sp. Gr. of Rocks. 
1st. 
Natural. 
2nd. 
Vitrified 
artificially. 
GENERAL LIMITS OF PROPORTIONS IN THE IGNEOUS ROCKS. 
1. Siliceous, 
62-78 
11-20 
3-6 
1-6 
1-2 
I- 2 
1-4 
2-3 
2-4-2-7 
235-2.46 
2. Basic, . 
45-58 
11-20 
1-3 
1-6 
5-12 
3-12 
7-20 
i-4 
2-8-3-2 
2*5 —2'84 
MEAN PROPORTIONS IN THE TWO MAGMAS. 
1. Siliceous, 
71-0 
16-0 
4'5 
2-5 
10 
1*0 
25 
1-2 
2'65 
2'40 
2. Basic, 
51 *5 
16-0 
ro 
3-0 
8’0 
6-0 
13-0 
1-3 
2 - 95 
2 72 
By combining the results I have obtained by chemical and mecha¬ 
nical analysis with those of analyses already published by various mine¬ 
ralogists, I have established that igneous rocks of crystalline texture, 
and almost all compact or vitreous masses, formed by fusion, and wrongly 
considered as minerals, are derived from one or other of these Magmas. 
To the first are referable all the Granitic rocks, including the Eurites, 
Quartziferous Porphyries, and Petrosilex, the Trachytes, Phonolites, 
Perlites, Obsidians, Pumices, and Lavas, wdth Yitreous Felspar. To 
