CHEMICAL RELATIONS OF THE VOLCANIC ROCKS. 
119 
A chemical analysis of the hornblende-trachyte ( 277 ) from Observation Hill gave 
the result under I.* With this is compared the analysis of the tephritic trachyte from 
Forodada under II, f and that of a trachydolerite (haiiyne-phono.lite) from Campanario, 
IH-t 
I. 
IA. 
II. 
III. 
(Observation Hill.) 
Mol. ratios. 
(Forodada.) 
(Campanario.) 
SiO„ 
= 
55-47 
•918 
56-19 
55-40 
TiCi, 
= 
1-32 
•017 
0-57 
0-43 
ALA 
= 
20-67 
•202 
20-25 
21-03 
FeA 
= 
2-83 
•018 
2-76 
1-64 
FeO 
1-86 
•026 
2-32 
3-04 
MnO 
= 
0-02 
trace 
CaO 
= 
3-43 
•061 
4-30 
3-57 
SrO 
= 
0-01 
MgO 
= 
1-43 
•035 
1-12 
0-91 
Na.,0 
= 
8-33 
•134 
6-33 
7-64 
Iv.,0 
= 
4-8G 
•051 
4-19 
4-42 
PA 
= 
0-03 
0-54 
0-23 
H.,0 at 110° 
= 
0-08 
0-65 
0-95 
FLO above 1 lo° 
= 
0-12 
( 
Cl,S0 3 etc. O' 25 * 
0-57 
100-46 
99-47 
99-83 
As in the case of the kenytes and the other trachytes, the analysis indicates the 
presence of nepheline which, however, could not be detected with certainty in the base 
of the rock. 
A determination was made of the silica-percentage of the altered yellow trachyte 
(278) from the top of Observation Hill and gave the result 56 "96. 
Chemical Relations of the Preceding Volcanic Rocks. 
For convenience of comparison the results of the analyses of seven of the rocks 
described in the preceding pages are brought together in the following table.§ 
Si0 2 
a.) 
(2-) 
(3.) 
HI 
(5.) 
(6.) 
HI 
= 
42-14 
43 ■ 92 
55-47 
55-93 
56-09 
57 ’ 95 
58-64 
TiO., 
= 
4-90 
4-19 
1-32 
0-64 
1-23 
0-40 
0-28 
A1A 
14-95 
17-42 
20-67 
19-61 
20-79 
20-43 
22-55 
FeA 
= 
2-90 
4-09 
2-83 
1-75. 
1-54 
3-43 
0-97 
FeO 
= 
9-71 
8-83 
1-86 
6-32 
3-84 
1-35 
0-99 
MnO 
= 
0-12 
0-09 
0-02 
0-13 
0-05 
0-07 
trace. 
CaO 
= 
10-32 
9-53 
3-43 
3-53 
3-18 
1-90 
1-43 
SrO 
= 1 
o-oi 
MgO 
= 
9-47 
4-89 
1-43 
0-50 
1-26 
0-26 
0-16 
Nn„0 
= 
3-27 
4-60 
8-33 
7-75 
7 * 33 
8-32 
9 "87 
K 2 0 
= 
1-80 
2-17 
4-86 
3 " 67 
3-91 
5-96 
4-98 
PA 
= 
0-40 
0-67 
0-03 
0-12 
0-38 
0-07 
trace. 
Cl 
= 
0-17 
H.,0 at 110° 
= 
0-12 
0-C6 
0-08 
o-io 
019 
0-23 
0-08 
11,0 above 110° 
= 
0-16 
0-11 
0-12 
0-19 
0-39 
0-39 
0-35 
100-26 
100-57 
100-46 
100-24 
100-45 
100-76 
100-30 
* For discussion of analyses see below, 
f Becke, l.c., p. 177. 
t Sauer, Untersuch. ii. pkonolit. Gesteine der Canarischen Inseln, Inaug. Diss., Halle, 1876, p. 60. 
§ The analysis of the glassy limburgite 326 is here omitted, since the result is almost identical with that of 
the holoerystalline olivine-hasalt 656. 
