264 THE PHYSICAL GEOGRAPHY OF AUSTRALIA. 



All these large water courses are filled to their utmost capacity during 

 wet seasons, but in dry years they have only a little permanent water 

 in them. 



Lakes. — Most of the so-called lakes of Australia are insignificant 

 depressions filled with the storm waters of widely expanding river 

 channels during heavy rains. In the central regions these are spread 

 out over extensive shallow basins, usually surrounded by a thick deposit 

 of mud, whose surface is characterized by a hard and treacherous 

 saline crust. Located in vast, rainless, saltbush country, where the 

 heat is intense, the flood waters evaporate with astonishing rapidity, 

 and for most part of the year these lakes are simply enormous mud 

 basins, where salt is deposited in large quantities. During the rainy 

 season they are again filled by the flood waters of inland rivers. The 

 largest are lakes Eyre, Amadeus, Gardiner, Torrens, Frome, and Greg- 

 ory, all more or less salt. The configuration of the continent is not 

 favorable to the formation or existence of large natural reservoirs for 

 the storage of permanent fresh water in the inland regions, such as 

 are to be found in New Zealand and other countries where deep lake 

 basins occur in mountain regions and on high table-lands. Formed, as 

 Australia is, like the inverted half of a gigantic bivalve, with the east- 

 ern part high and dipping more rapidly toward the center than the 

 western half, which gradually and imperceptibly slopes inward, most 

 of the inland basin is flat, the soil and upper stratum highly absorbent, 

 while the lower portion of the bed in several parts is not much, if 

 indeed at all, above sea level. For this reason, and in view of the 

 general physical structure of the continent as a whole, I regard the 

 theory of subterranean channels, through which it is believed that large 

 volumes of rainwater find their way to the sea, as altogether erroneous. 

 No leakage of sufficient magnitude to compensate for the somewhat 

 rapid disappearance of the flood waters of some of our inland rivers, 

 in my opinion, exists, and the convenient supposition, for such it really 

 is, that the few and insignificant submarine springs between Cape 

 Otway and the mouth of the Murray River are indicative of such, 

 arises more from a preternaturally excited imagination than from a 

 just conception of the fundamental law of hydrology. Several so-called 

 leakages no doubt occur along some parts of the coast line, oozing 

 through the porous strata or in the form of bubbling springs, such as 

 may be met with along the shores of most of the Pacific islands, but 

 the necessary evidence to sustain the theory that large volumes of 

 fresh water are discharged into the ocean through subterranean chan- 

 nels is not at present available. 



Flood waters are usually highly charged with sediment that is held 

 more or less in suspension while they pass through channels of steep 

 declivity, but which is rapidly deposited over areas where the minimum 

 velocity occurs. The primary effect of deposition is experienced in the 

 rapid or gradual silting up of water channels, and consequent dimiuu- 



