d2 ARCTIC BASALT PLATEAU 
The alternating eruption took place during a distinct period of 
rhythmical continental upheaval in such a close alliance the former 
with the latter, that it is difficult to separate the cause from the 
effect. The mode of eruption, being a fissural one, points toward 
a deeper magmatic action as the cause of upheaval and eruptivity; 
the fissures, which generally do not represent faulting lines, were 
opened from downward by upward pressure, and, meeting on their way 
upward stripes of pronounced weakness formed by ancient deepseated 
valleys, they do not reach the main plateau surface, at least not by 
their volcanicity; the latter finds its outlet in pouring down the valleys. 
The plateau behaves as a uniform block, and the uniformity 
of volcanics seems to stay in connection with this beha- 
viour. In places where the fissures develop into veritable faul- 
ting lines, with differential and opposed movements on both sides 
of the line, the volcanics seem to become more variegated, specially 
in cases where the faults are manyfold and the blocks between them 
become tilted (New Siberian Islands with Bennet Island).? 
It is to be controlled if this statement is to be valid for the At- 
lantic half. Few significations may satisfy. 
De Geer states, in his memoir upon the physiography of Spits- 
bergen,” that a zone of diabasic eruptions trends „from SE to NW 
as a diagonal through the region of the present Ice Fjord, separa- 
ting the main fjord from the diverging four inner branches‘. The 
diabases are very uniform ones, and this zone marks a distinct 
flexure of upheaval. The Stor-fjord line of diabases, running in 
1 From the standpoint developed above even simple faults, accompanied by 
differential movements and volcanic action, may, in consequence, depend 
upon movements and actions of a different kind in the subcrustal magma (astheno- 
sphere) as compared with the upward movements beneath the plateau; and con- 
cluding from uniformity of force to homogeneity of acting material the logic compels 
one to suppose a diversity of deepseated material in connection with irregular mo- 
vements; thus the alkaline character of rocks seems by no means to be obliged to 
assimilation of country rocks, but can appear independent. 
2 G. De Geer, On the physiographical evolution of Spitsbergen. Geografiska 
Annaler 1919. 2. pag. 164 (Stockholm). 
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