88 



Balaklava was onlj at about tlie rate of half a mile in 24 liours, 

 and frequently the head of the flood remained stationary for 

 half an hour whilst it poured into one of the many large 

 fissures in the river bed. Two years ago it was noticed that 

 the E-iver Avoca, in Victoria, required a period of ten days to 

 flow along one of its lower reaches about 27 miles in length, or 

 only a speed of about two and three-quarter miles per day. 



This water, lost by our rivers on the plains, enters the 

 ground and percolates vertically, and laterally to a greater or 

 less distance, according to the permeability of the beds under- 

 neath or the existence of old river channels, which, in some 

 instances, allow of lateral percolation to a still greater distance 

 from the river. 



This lateral percolation, and the gradual increase of depth 

 from the surface of the line of saturation, may sometimes be 

 traced with considerable distinctness ; as, for instance, on the 

 plain of Adelaide, the Kiver Torrens appears to percolate 

 laterally under the city of Adelaide, and it was noticed a few 

 years ago, after the Torrens dam was filled, the water supply 

 in wells in Adelaide at or below the river level was much larger 

 than before. The Eiver Torrens also percolates through Fin- 

 don as far as AYoodville, about two miles, and, most probably, 

 in one or more old river beds ; but, on crossing the Port-road, 

 about one mile farther we come into dry country, which seems 

 to be outside the limit of percolation. In the hills it is most 

 probable that the lateral percolations from the creeks and 

 s?maller watercourses in the numerous gullies almost intersect 

 each other ; and if this is so, the area of underground water 

 below the lines of saturation will be almost continuous. In 

 all cases, however, the hydrogeological features of each locality 

 will require to be carefully examined and studied before explo- 

 rations for underground waters are undertaken. 



In the alluvial deposits of our plains these subterranean 

 waters generally saturate the permeable beds, and then collect 

 and flow in the beds of sand and gravel overlying the clays or 

 other impermeable beds. In the ranges they are found in 

 small streams in the fissures of the quartzites and other harder 

 rocks, and saturating the sandstones, and passing through the 

 bedding and, I think, the cleavages of the shales and clay 

 slates, and are met with by boring or sinking in the form of 

 small feeders rushing out in spray form, or in considerable 

 streams, according to the size of the fissures and the height of 

 the source above the point of outlet. 



Assuming these deductions as to the great loss by percolation 

 in the hills to be correct, we may conclude that the strata 

 underneath our numerous and extensive mountain ranges below 

 the lines of saturation form one almost continuous under- 



