Page:A Treatise on Geology, volume 2.djvu/107

The differences of the ultimate analysis are very much smaller than the different aspect of the rocks might lead us to expect.

Sienite, composed of quartz, felspar, and hornblende, in equal proportions, would be represented in the subjoined table by column 1.; sienitic granite in which quartz, felspar, and mica should appear in equal proportions, in column 2.; schorl rock, composed of equal parts of quartz and schorl, in column 3.

1.

2.

3.

Silica

69.91

63.96

68.01

Alumina

10.37

14.32

17.91

Potash

4.55

5.94

0.35	$\left.{\begin{matrix}\ \ \end{matrix}}\right\}$	soda.
0.98

Lime

4.86

3.73

0.14

Magnesia

6.26

5.94

2.22

Oxide of iron

2.69

4.06

6.85

Oxide of Manganese

0.07

0.21

0.81

Fluoric acid

0.50

0.65

1.79

Turning from these rocks, in which quartz is an essential constituent, to those which are composed of felspar united with hornblende or some analogous mineral, we have greenstone (felspar and hornblende in equal parts) represented in the first column of the next table;

	1.	2.	3.
Silica	54.86	59.14	58.42
Alumina	15.56	10.59	13.86
Potash	6.83	6.83	9.10
Lime	7.29	1.13	4.87
Magnesia	9.39	7.00	8.13
Oxide of iron	4.03	12.62	2.00
Oxide of Manganese	0.11
Fluoric acid	0.75
		0.50	1.06