432 T. W. E, DAVID. 
has given rise to many conjectures but no certain proof. In 
opposition to the hydrostatic pressure theory I would suggest the 
great dynamical effects of the contraction of the earth’s crust 
acting on the superincumbent as well as subterincumbent strata, 
as offering a more probable solution of the cause and origin of 
artesian supply. Geologists tell us that this contraction accounts 
for the flexures of the earth’s crust and strata, and for fractures 
and earthquakes, even for climatic changes. The evolution of the 
earth’s features is therefore almost controlled by it. This con- 
traction induces lateral pressure, which acting in a horizontal 
direction produces those flexures which originate mountain chains 
and valley depressions. Its effect has been distinctly proved by 
geological science to have occurred at different periods up to and 
even after the lignitic period of the Tertiary. The action of the 
wind on the sea gives in a modified degree some impression of the 
effect of this contractive force on the earth’s surface. Now 
artesian basins, whether of large area, as in the Cretaceous System, 
or of smaller dimensions as in the Tertiary, represent in their 
overlying strata a series of broad tabular masses which are 
subject to very gradual flexure by this lateral pressure inducing a 
depression in the centre, and it is this force combined with expan- 
sion from heat which causes artesian supply in most instances 
rather than hydrostatic pressure. Lyell calculates that sandstone 
one mile thick raised in temperature 200° Fahrenheit, would have 
its upper surface elevated ten feet, showing the great force of this 
expansion. Professor Tate’s paper, recently read in Adelaide, 
seems to me somewhat to strengthen my conclusions. He premises 
that the isolation of West from East Australia which existed 
while Central Australia was a marine area was partially continued 
into late Tertiary times, not by geological but by climatic con- 
ditions, first by the conversion of the depressed area into a vast fresh 
water sea to be followed in our own time by utter desiccation. In 
my opinion it is this fresh water sea, or contemporaneous inland 
lakes, filled in by the wasting and erosion of surrounding strata, 
and then completely sealed by a siliceous crust probably formed 
