290 
where the depression reaches its maximum, a subsidence amount- 
ing to about three kilometers may be postulated. 
Age of faults in relation to the Plutonic rocks. — It is 
evident from direct observations that the main faults are younger 
than both the sandstone and the undestroyed part of the vol- 
canic series. The absence of these formations outside the 
sunken area is easily explained as a consequence of the de- 
nudation. It is, however, a very remarkable fact that intruded 
abyssal rocks, which have risen to considerable heights within 
the area of subsidence, are nowhere visible in the adjacent 
Fig. 26. Reconstructed cross-section of the Ilimausak batholite. 
Scale of lengths and heights 1 : 260000. 
a Algonkian granite. — b sandstone. — с volcanic sheets. — а Plutonic rocks. 
(The position of the section is indicated on the sketch map, Fig. 95. 
tracts, and this notwithstanding that natural sections down to 
sea level are found in many parts of the district. This would 
seem to indicate that the main faulting is not later than the 
consolidation of the batholites, and a closer examination will 
corroborate this view!. 
The relation of the faults to the batholitic rocks can be 
best studied along the great southern fault. This fault, as 
previously mentioned, is very conspicuous south and southwest 
! Here only the main faulting is considered. The first beginning of the 
crustal deformations may perhaps have preceded the first manifestations 
of the late Devonian igneous activity, but, as discussed in the descrip- 
tion of the structure of the Ilimausak batholite, subsidence in some 
places may have continued after the consolidation of some of the ba- 
tholitic rocks. 
