24 : ARCTIC BASALT PLATEAU 
thus giving a slightly erroneous idea of the true character of the 
rock. It was stated above that the mafic minerals predominate, 
the „norm“, on the contrary, states a slight predominance of salic 
constituents, since all lime and alumina are drawn to the salic 
group, though a great part of them is mafic. The figures of Osann 
enlisted above give a picture of more concordance with the true 
proportion, the great value of f being significant. 
The classification of this rock presents some difficulty. Above 
analyses of two rocks irom the western Arctic basalt region are 
tabulated, but they differ in lower alumina content and in high 
alkalies, specially in potash. Moreover, in the Jan Mayen rock 
lime dominates over magnesia, thus the salic characteristic is more 
salient and the rock pointed out as alkaline by the normative (and 
actual) nephelite content; the same is valid to the Mt. Halvdan 
rock only on part of alkalies, all these marks being absent in the 
Bennet island-rock. Yet a comparison is made, because the high 
alumina does not conform with the demands of proper basalt. 
It is seen, that whilst in the early magmatic stage of the rock 
the progressive crystallisation marked a decreasing lime content of 
the salic constituents (plagioclase), yet the late magmatic stage 
continuing in the postmagmatic creations marks an inverted deve- 
lopment with increasing lime content to the end of crystallisation, 
partly issued after the complete consolidation of the rock. If the 
inversion point, marked by the hiatus in cristallisation between 
plagioclase low in lime and analcite, is to be pushed backward to 
the earlier magmatic stage, or, in other words, the rock magma in 
early stage of crystallisation is to be supersaturated with a rising 
quantity of overheated steam, then the zeolite phase of the rock 
will begin before the groundmass is solidified (this moment being 
pushed forward) and a part of the minerals, specially these which 
are alkalibearing, will be bucked out and deposited in steam cavities, 
whilst the minerals richer in lime partly resist and partly alter in 
zeolite; this alteration in case of plagioclase —> thomsonite is ac- 
