THE VOLCANOES AND ROCKS OF PANTELLERIA 707 
These analyses resemble those of the preceding type in most 
respects, but differ in the higher soda and in the relative amounts 
of the iron oxides, ferrous oxide being here largely in excess of 
ferric, both in percentage and molecularly, though the sums of 
the two in both types remain about the same. Foerstner’s analyses 
show the same relations to mine as in the previous cases, a tendency 
to lower alumina, and- higher ferric oxide, magnesia, lime, and 
soda. Except in E his ferrous oxides are higher than ferric, or 
nearly so. I could detect none of the copper noted by him in any 
of my rocks. 
Norms.—The norms of my analyses are as follows: 
A B C D 
(O)s.0 vin 80 6, So eee 28.38 14.70 28.02 15.36 
lies bone oom ee 27.80 28.36 27.80 28.36 
JANIS)»: on: aco's 9 Sehgal tee eee 17.82 33-54 17.82 39.30 
EN@o:6°0 lo ear ROC Rte Eee ee 5.08 6.01 7.85 5-54 
IN [8\o 9 5.9.01 ge CRO eee 7.08 ALS SeLy Ti. 22 
ID os d:</0nG EL ee ene 0.75 1.24 2.16 oe 
ISW75, o Bbc 0 Uo oan eee 10.34 Q.o1 9.28 7.80 
IN o-cie die chee ce eee eee "7 TO 1.67 TS 2 
EN 0) ck Sues SC SRE 0.34 0.34 mittot 0.34 
98 .96 99-17 97-77 99.44 
IRESE ao rc 6-6-0 CUS OR Eee 0.35 0.81 2.62 0.15 
99.31 99.98 100. 39 99.59 
These norms are noteworthy because of the large excess of 
soda, expressed as sodium metasilicate, over alumina and ferric 
oxide, which they show. This finds expression modally in the 
presence of cossyrite, and study of the thin sections shows that, 
in a general way, the amount of cossyrite present is correlated 
with that of sodium metasilicate in the norm. The analysis of 
cossyrite by Dittrich’ yields nearly 9 per cent of sodium metasilicate, 
and it is also very high in ferrous oxide. These two factors deter- 
mine the chief chemical differences between the two main types 
of pantellerite—the one with dominant aegirite and the other 
with dominant cossyrite among the mafic minerals. 
These norms show that all the rocks are in dosalane. The 
Gelkhamar and Cantina Ziton rocks fall in varingose, transitional 
1 Cf. J. Soellner, Zeits, Kryst., XLVI (1909), 530. 
