380 TRANSACTIONS OF SECTION C. 
beds also of the Dwina system. In South America the Lower Rocks of the 
Santa Catharina system appear to be more Permian than anything else, and 
the occurrence of the strong swimming reptile Mesosaurus both in the Permo- 
Carboniferous rocks of South America and of South Africa suggests that the 
South African Permo-Carboniferous rocks also may be chiefly Permian. 
In the correlation of the Australian Permo-Carboniferous formations, special 
emphasis is laid on the Indian facies of the West Australian Permo- 
Carboniferous fauna. 
2. The Great Australian Artesian Basin and the Source of its Supply. 
By E. F. Pirrman. 
3. The Geological Relations of the Artesian Water-bearing Beds of 
Southern Queensland. By S. Dunstan. 
4. The Post-Jurassic Geography of Australia. Notes on the Hypothesis 
of Isostasy. By EK. C. ANDREWS. 
The doctrine of isostasy implies the general correspondence, in weight, of all 
vertical columns of unit size composing the Earth’s crust to a depth known as 
the depth of compensation. This depth is taken at 122 kilométres below sea 
level by Hayford.1 
The excess of height of the unit columns, in continental areas, is con- 
sidered as being compensated by the excess of crustal density in suboceanic 
areas. Isostatic compensation is supposed to follow rapidly upon loading and 
unloading. Examples of such loading are sedimentation and the formation of 
a continental Ice Sheet, while examples of unloading are erosion and _ the 
disappearance of an Ice Sheet. The adjustment is considered to be a gradual, 
rather than a spasmodic, process. Anomalies of gravity, however, are recorded 
from many localities, and Gilbert? suggests that the explanation of such is 
to be sought in nucleal heterogeneity. 
Geography.—Kast and West Australia form two positive, or buoyant, ele- 
ments, while the Inland Plains, in the main, represent a negative, or sunken, 
area. With these three elements should be considered New Zealand, Malaysia, 
the South Pacific, the Indian, and Southern Oceans. 
During Cretaceous time a great plain of erosion appears to have been 
formed in the positive elements of Australia, while the extensive epicon- 
tinental sea of that period was filled with the waste derived from the neighbour- 
ing erosion. Subsequently, both the old plain of erosion and the northern 
portion of the area of sedimentation were elevated to a moderate height and 
a long period of equilibrium and erosion ensued. This sequence of elevation 
and of pauses of equilibrium with erosion was repeated until the close of 
the Kosciusko Period,? the pauses between the uplifts becoming less impor- 
tant, but the amount of vertical movement becoming correspondingly emphasised. 
At various stages of the process basalts flooded Eastern Australia, especially 
in areas of older sedimentation. The appearance of the old basalt-covered 
stream-drifts is suggestive of a temporary subsidence for the plateau areas 
during the basaltic period. 
Strong streams, such as the Shoalhaven and the Hawkesbury, maintained their 
general courses against the uplifts along their lower portions. Hence it is 
inferred that the uplifts were effected slowly, nevertheless the periods of equi- 
librium separating the revivals of elevation were of much longer duration than 
the uplifts themselves. 
* Hayford, J. F., ‘ Figure of the Earth and Isostasy,’ U.S. Coast and 
Geodetic Survey, Washington, 1909. 
? Gilbert, G. K., ‘Interpretation of Anomalies of Gravity,’ U.S. Geo- 
logical Survey, Washington, 1913. 
* Closing Tertiary. 
