28 
ground, as the rain falling upon this outcrop soaks away down to be imprisoned 
between the impervious beds, and stands at a certain elevation, according to the 
natural obstructions in the way of its passage towards the sea. Should this water 
level be above the level of the country where the impervious beds overlay the 
water-bearing stratum, then it is an artesian area, for if a shaft is sunk down to : 
the water-bearing bed, the water will rise above the surface, or if confined in tubes 
it will rise to the same level in the tubes as the water is standing in these beds 
on the higher ground. 
Another question on which there seems to be a good deal of confusion is one 
of dynamics; a column of water a certain height gives a certain pressure to the 
square inch; no matter the size of the column the pressure will be exactly the i 
same, as it is only the vertical pressure of the water which is perceptible. For 
example, the pressure on the pipes in Perth is only equal to a column of water I 
standing at the same level as the water in the reservoir. This question of pres¬ 
sure is generally confounded with supply; for instance, a pipe 20 feet high filled | 
with water gives a certain pressure; now replace the top four feet with a tank 
filled to the top, the pressure remains the same, but it will take much longer to I 
run all the water oif. Multiply these columns and tanks to any extent, connect¬ 
ing them all at a common junction, then take the pressure, when, if the surface of 
the water still stands at 20 feet above the point where the testing is done, the 
pressure will be exactly the same as the one single pipe of water of the same ! 
vertical height. 
A basin when spoken of in the artesian sense refers more to the geological i 
formation than to the surface, for an artesian supply may be obtained on the top 
of a hill, provided the water-bearing beds outcrop at a still greater elevation. 
The question of artesian areas is therefore most complicated to one who has | 
never studied the subject, for although basins are always talked about, no suck , 
things are found at the surface and rarely in the rocks themselves, which arc 
generally folded into a cynelinal trough, into the centre of which the water is 
thrown, and along which it gradually percolates towards the sea. 
Some years ago the idea was started of obtaining artesian water on the 
Yilgarn Goldfield on the grounds that it was a basin-shaped depression, with 
high ground all round. The arguments used in support of the idea were of 
the class that artesian water existed in the interior of the other colonies near the , 
salt lakes. Some people went even so far as to state that water would be struck at 
1,000 feet, as the pressure of the rocks would cause the water to rise, forgetting 
that a corresponding pressure would be required to force the water down. 
Let us consider the Yilgarn District. We know that wherever mineral veins 
exist the country must be more or less broken; in fact, lodes are fissures, cithef 
running with or across the country ; whilst the bedding of the rocks in this district 
is, as a rule, inclined at a veiy high angle, sometimes dipping even vertically* 
The pervious beds, therefore, as well as the impervious ones, outcrop, and if wateV I 
existed in them under pressure it would have to overcome no obstacles in its 
way to rising either in the beds themselves or up the fissures, and so making it# 
escape at the surface. 
The mistake into which many well informed persons have fallen in this district 
is that, Istly, it is basin-shaped; 2ndly, pervious beds outcrop on the highland 
(sandplains) ; drdly, impervious beds are met with at the surface on the low ground 
(lake beds) ; therefore, if bores were put down through these, artesian water would 
be obtained, Unfortunately for this argument, the sandplains are only capping^ 
and do not underlie the clays of the lakes, which rest directly upon the upturned 
edges of the old rocks, and when sunk through prove that they overlay a large 
water supply, but which unfortunately is extremely salt, and is not under any 
pressure, so that no artesian water exists. 
