920 _ W. R. BROWNE. 
How the east-flowing’ part of the river came into being 
is undoubtedly puzzling. The presence of conspicuous | 
jointing ina direction nearly east and west, already noted, 
may indicate an east and west fault or buckle along the line 
of the river. At all events there is a downward slope from 
the divide to the river. fi 
It is a noteworthy fact that while some of the valleys, 
as for example those of Pilot Creek and of the old Murrum- 
bidgee south of McCarty’s Crossing, are marked by flows 
of basalt, others such as Dairyman’s Plain and the valley 
between Mittagang and the §S-bend are quite free from — 
basalt. It may be that certain of the valleys were more 
conveniently placed than others with regard to the centres _ 
of eruption, for flooding with lava. 
From the depth to which the relatively mature valleys ; 
such as that of Pilot Creek have been eroded in the Berri- 
dale fault-block, and the fact that this valley when it 
emerges along the Mittagang road from the fault-block 
suffers no change of level, and from consideration of the 
fact that the valley between Mittagang Bridge and the S- 
bend is at its northern end on about the same level as the’ 
topmost alluvial terrace at the bend, one is inclined to- 
believe that the fault-block rose very gradually, the erosion ° 
of the southward-flowing stream keeping pace with the 
elevation, until the formation of the new divide tilted the 
country down somewhat towards the north and caused the 
formation of the present Murrumbidgee gorge through the 
fault-block. Itis probable that the upheaval which caused | 
the present divide gave the country a bit of a tilt to the 
north-east. 
Age of the basalts.—A very interesting question is raised 
by the foregoing discussion, with reference to the exact 
period of outpouring of the basalts. Such basaltic eleva- 
tions as Tillabudgery and The Brothers probably antedated 
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