30 ARCTIC BASALT PLATEAU 
maxima of volcanicity, the latter being in high degree dependent 
on the-depth and number of the dissecting valleys. Comparing the 
absolute heights of the plateau, and combining them with the migh- 
tiness of the basalt piles and with the number of separate flows a 
‘ line may be drawn, which runs from the upper Piasina region in 
the north to the Tunkin Alps in the south and which may in gene- 
ral correspond to an axis of the greatest upheaval (fig. 2). This 
axis of the greatest upheaval coincides to a great extent 
with the ancient valley depicted above and hence the great 
development of volcanicity along this line may be explicable. 
@ Basalt 
e— + Axis of maximal upheaval 
Fisk 
As to the cause of these upheavals the thought of isostatic read- 
justment lies at hand. Yet there is no distinct region of subsidence 
in the neighbourhood, that could be taken into consideration as a 
compensating area, the nearest lying too far away and being separated 
from the plateau described above by broader zones of tectonical weak- 
ness. Moreover the uniformity and the flatness of the (northern) area 
does not favour such a strong and accelerated denudation, as may be : 
expected in areas of uplift. In all, a rhythmical uplift, at well defined 
intervals, may hardly find its explication in isostatic readjustment alone. 
