Specific Gravities. 
Principal Types of Igneous Rocks. 
Natural. 
Vitri 
Limits. 
Mean. 
fled. 
Granites,. 
/ 2*60 1 
( 2-73 / 
2-66 
2-39 
Granitic 
Group. 
Eurites,. 
/ 2 58 1 
12-70/ 
2-64 
2-36 
Petrosilex,. 
/ 2*58 1 
\ 2-68 / 
2-64 
» 
& 
” Trachytes,. 
/ 2-601 
\ 2-70 ) 
2-67 
ff 
a 
o 
Ph 
Trachytic Lavas, .... 
/ 2-58 | 
12-64/ 
2-62 
2-46 
§ J 
O 1 
g 
Phonoliths,. 
{ - } 
2-58 
ff 
ts 
CQ 
Trackytic 
Trachytic Porphyry,. . . 
/ 2-52 1 
12-65/ 
2-58 
ff 
Group. 
Pitchstones and Retinites,. 
/ 2*311 
12-36 / 
2-34 
ff 
Perlites,. 
(2-341 
1 2-40 / 
2-37 
ff 
Obsidians,. 
/ 2-25 1 
12-55/ 
2-40 
2-34 
^ Pumices, . .. 
/ 2-00 1 
12-53/ 
2-30 
2-46 
Degradation 
of Siliceous 
Rocks. 
1 
Trachytic. 
Syenitic Granites, .... 
Andesites,. 
1 
/ 2-631 
12*75/ 
/ 2-58 1 
12-72 } 
2-68 
2-67 
2-45 
ff 
3 
Ancient. - 
( Syenites and Syenitic Por- 
{ phyries,. 
(2-67/ 
12-78 j 
2-73 
ff 
o 
f Trachydolerites, .... 
/ 2' 70 1 
1 2-85 } 
2-78 
ff 
? ‘ 
Modem. ^ 
| Ferrocalciferous Retinites, 
1 Perlites, and Obsidians, 
} 
2-40 
2-49 
w 
i 
Ferrocalciferous Pumices, . 
to to 
di o 
-1 o 
2-30 
>> 
1 
Diorites,. 
/ 2-80 1 
| 3-20 J 
2-95 
2-66 
Euphotides,. 
/ 2-85 1 
\ 3*10 j 
2-95 
2-62 
Hyperites,. 
2-85 1 
1 3-10 } 
2-95 
ff 
Melaphyres,. 
( 2 75 1 
1 2-95 } 
2-85 
2-60 
Basic Rocks. < 
Basalts,. 
/ 2-851 
1 3-10 } 
2-96 
2-84 
Dolerites,. 
/ 2-851 
\ 8*10 } 
2-95 
ff 
Pyroxenic Rock, average 
f » l 
2-92 
composition,. 
1 >» / 
ff 
Doleritic Lavas, .... 
/ 2-851 
1 3-00 } 
2-92 
2*75 
Leucito-augiticalciferous 
/ 2-72 1 
2-80 
lavas,. 
1 2*90 / 
ff 
Degradation of Ba¬ 
sic Rocks. 
Serpentines,. 
/ 2-501 
12-66/ 
2-58 
ff 
The double c 
