136 THE ROMAN COMAGMATIC REGION. 
Ratios. 
I. II. 
Sal 
Class ...................... ^ =1.60 1.56 
Fern 
p 
Order ...................... -- =0.18 0.50 
r - 3-7 
Analyses I and II are much alike, the differences being of small importance. It 
will be noticed that their norms are unlike in that the norm of I shows considerable 
akermanite, while that of II shows no akermanite, but a little orthoclase, and con- 
siderably more anorthite and less leucite. These are explained by the slightly 
lower silica and higher lime and potash of I. The two resemble the analysis of the 
romal albanose (p. 130), but not as closely as they do each other. In the former 
type the alumina and potash are considerably lower and the lime and magnesia 
higher. 
The analyses in III and IV are not very reliable. It may suffice to point out, 
as very doubtful features, the high alumina and low magnesia, the iron oxides, and 
the high potash, as well as the presence of copper in III. Copper was especially 
looked for in my analysis of the Pofi rock, but without finding even a trace, and it 
is probable that the copper reported by Speciale is in reality platinum derived from 
the vessels used. In IV may be noted the somewhat high silica, the iron oxides, 
the high lime, and the unsatisfactory summation. It may be noted that the magma 
represented by this analysis would fall in II. 6. 3. 3,* an improbable position for 
such a highly leucitic and feldspar-poor rock. 
Mode. Neither of the specimens lent themselves to microscopic measurement, 
on account of the fineness of the grain and the difficulty of estimating the leucite 
and interstitial substance. As the simpler one the mode of the Pofi rock will be 
discussed first. This calculates out as follows: 
Anorthite, Ab,Ani S .............................. 14.1 
Leucite ......................................... 35 
Nephelite ....................................... 5.1 
Augite .......................................... 41.0 
Olivine ......................................... 4.0 
Ores ........................................... 0.5 
Apatite ......................................... 0.3 
100. o 
This mode corresponds well with the appearance of the thin section, though 
the amount of anorthite is rather larger than one would expect. The adjustments 
are of comparatively slight importance, chiefly to form the augite, and those necessary 
to change orthoclase to leucite, with consequent formation of a little albite and less 
nephelite. The mode therefore may be regarded as normative and the rock 
described as normative alferphyri-albanose. 
* Washington, Prof. Paper, U. S. Geol. Surv. No. 14, 1903, p. 301. 
