42 ARCTIC BASALT PLATEAU — 
the capping basalts in this part have a much lesser spreading than 
may be concluded from the sections on the Angara river, asides 
from the principal valleys the basalt failing quite. 
The points of outburst of the basalts are unknown. The ancient 
„volcanoes“ pointed out in the upper Lena river region (by Gue- 
rassimoff a. 0.) play a subordinate role and have not any impor- 
tance upon the wider distribution of the basalts being local short- 
lived outbreak-points of lava without considerable tuff production. 
A closer examination! of the basalt-lined valleys of the north 
reveals at irregular intervals oblique or vertical offsets of basalt 
dikes of different thickness, which do not in general produce any 
greater disturbance in the horizontal strata than a local upbending, 
occasionally witn included greater rock fragments; on both sides of 
such an upbending the strata redeem their original position at a 
short distance from the dike without any relative displacement being 
visible. These fissures seem to have no greater connection with 
structural lines in general and they get lost in the vaste bordering 
plateau land without any sign of volcanic action except the related 
one on both sides of the river bed, at some height from from the 
bottom and at some distance downstreams. - This statement is valid 
for broader valleys of greater age. On the tributary valleys of lesser 
importance and greater youth the basalts fail and the canion-shape 
disappears. If the offsets of basalt are arranged closer together, the 
basalt beds corresponding each to an offset join building up a 
uniform formation of constant level, without visible discordance, 
and line the canon-shaped valley on both sides. If, in exchange, 
the offsets are distant each from the other, the tracks of volcanic 
action are less significant, the belonging basalt bed rests within 
small dimensions and is oiten eroded away, leaving a basaltic tres- 
1 The following statements are in general based upon observations made by the 
writer during several crossings of the plateau north off the Lower Tunguska river 
(cf. H. Backlund, „La Géographie" 1907. Paris) and upon studies of travel- ‚reports 
(Maack, Czekanowski, F. Miiller a. o.). ° 
