TABLE II. 
To face page 162. 
Principal Types of Igneous Rocks. 
Specific Gravities. 
Limits. Mean. 
Mean. 
Limits. Mean 
Limits. Mean. 
Magnesia. 
Oxides of Iron 
and Manganese. 
Loss by 
Ignition. 
Limits. Mean. 
Granites, 
SS? ]"•*■ ' 
^ Petrosilex, , 
: 2-601 
. 2-73 ; 
'2-581 
2-70 j 
' 2-58 1 
2-68 J 
2-64 
2-39 || ” 
2-36 
75-4 
15-3 
14- 5 
15- 0 
2-0 
2-0 
2-5 
0-5 
2-5 
1-5 
4-0 
0-5 
4-5 
Trachytic 
Group. 
' Trachytes, . 
Trachytic Lavas, . . . 
Phonoliths, . 
Trachytic Porphyry, . . 
Pitchstones and Retinites, 
Perlites, . 
Obsidians, . 
Pumices, ...... 
r 2-60 ■ 
2-70 
'2-58' 
i 2-31 
[2-36 
12-34 
2-40 
2-251 
.2-55; 
2-00 1 
. 2-53 J 
2-67 
2-62 
2-58 
2-58 
2-34 
2-37 
2-40 
2-30 
2-46 
2-34 
I 64 
71 
66-5 
710 
17-0 
17-2 
20-6 
13 5 
15-0 
13-0 
0-5 
6-0 
4-0 
8-0 
3-0 
14-0 
1-5 
7-0 
1-5 
11-0 
11-0 
2-0 
2-0 
2-0 
f-0 
To 
To 
1-5 
5-0 
1-5 
4-5 
1-0 
3- 0 
1-0 
4- 0 
t-5 
2.-5 
20 
60 
0-5 
4-5 
Trachytic. 
Syenitic Granites, 
Andesites, . . . 
J 2-631 
1 2-75 J 
< 2-58 1 
\ 2-72 I 
2-68 
2-67 
69-0 
65-0 
15-0 
15-0 
2-0 
4-0 
5-0 
Ancient. 
Modern, 
( Syenites and Syenitic Por- 
\ phyries,. 
{ Trachydolerites, .... 
Ferrocalciferous Retinites, 
Perlites, and Obsidians, 
Ferrocalciferous Pumices, . 
{sn 
{&} 
/ 2-001 
l 2*57 / 
2-73 
2-78 
2-40 
2-30 
69-0 
15-5 
17-0 
8-7 
14-0 
2-0 
6-0 
3 0 
7-0 
2-5 
5-0 
4-0 
7-0 
10-0 
5-0 
12-0 
30 
110 
7-0 
9-0 
8-0 
Basic Rocks. 
Diorites, . . 
Euphotides, 
Hyperites, . 
Melaphyres, 
<J Basalts, . . 
Dolerites, . 
Pyroxenic Rock, average 
composition, . 
Doleritic Lavas, .... 
Leucito-augiticalciferous 
lavas, . 
’ 2-80' 
3-20 
l 2-85 
3-10 
I 2-85 : 
[3-10 
1 2-75 : 
2- 95 
12-85 : 
[3-10 
1 2-85 ' 
3- 10 
2-85 
; 3-00 
’2-72' 
;2-90 
2-95 
2-95 
2-95 
2-85 
2-96 
2-95 
2-92 
2-92 
2-62 
2-84 
2-75 
53-2 
52-2 
48-0 
50-2 
160 
15- 0 
14-5 
21-6 
13- 8 
14- 0 
16- 5 
15- 5 
16- 6 
0-5 
4- 0 
1-0 
3-0 
2-0 
6-0 
2-0 
5- 0 
2-0 
5-0 
1-0 
4- 0 
5- 0 
80 
0 
5-0 
9-0 
4-0 
8-0 
7-0 
14-0 
7-0 
13-0 
13-0 
6-0 
12-0 
6- 3 
9-5 
7- 6 
6-2 
10-2 
10-0 
8 - 8 
10-0 
9-0 
20 
10-0 
70 
15-0 
6-0 
14-0 
3-0 
5 0 
3-0 
10-0 
3-0 
4-0 
7-0 
1-0 
6-0 
10-0 
20-0 
8-0 
14-0 
80 
19-0 
5-0 
12-0 
9-0 
160 
9-0 
180 
100 
170 
60 
120 
14-0 
11- 5 
14-0 
9-0 
13- 8 
14- 7 
12- 5 
14-5 
9-2 
Degradation of Ba¬ 
sic Rocks. 
Serpentines, 
34-0 
44-0 
39-5 
3-4 
130 
The double commas, in this Table, denote percentages less than one-half. 
