MODE OF EXTRUSION 49 
Much has been written about the contemporaneousness of these 
basalts. Suess (l. c.) states, that while some flows crown the upper 
edge of the valleys, others have run down along the bottom; from 
| this he concludes, that they are not contemporaneous in a stronger 
sense, but owe their outbreak to a uniform geological process. Of 
this process he makes no decisive statement, yet he enumerates 
with coascientiousness the presumptive „volcanoes“, or centres of 
eruption, and mentions the possibility of fissural one. 
On base of the Statements above it is possible to give a picture 
of the mode of extrusion of the basalts confirming the uniformity 
of the connected geological process as follows. Towards the end 
of the Angara-time the continent being almost completely base- 
levelled began to rise. The river erosion immediately reinforced 
began to cut down deep valleys, a stagnation of the rise contributed 
to a development of broad river plains whither the flora migrated 
down, whilst the capping younger sediments of the uplifted area 
began to be eroded away. 
At that stage the first basalt lava breaks out from fissures, which 
seem to set up from downward, under an upward pressure, and 
these fissures meeting on their way through the uniform sediment 
plateau the deep-seated valleys open and pour out a portion of 
lava, but seem never to reach the main surface, or if so, the im- 
mediate output of basalt in the valley seems to hold the main lava 
surface on a level under the main plateau surface. If the flow was 
uniform, the river keeps back its original course and the erosion 
is reinforced anew, because an increasing rise, besides the uplift of 
the river bed by the basalt layer, immediately succeeds the basalt 
eruption, continues during the accelerated throughcutting of the 
basalt and of the floorrock and dies away by forming a new but 
somewhat smaller river plain. Then the process is repeated with 
alternating basalt outbreaks and maxima and minima of uplift. 
Not everywhere the maximum of upheaval seems to be equal. 
Yet the maxima of upheaval do by no means coincide with the 
