BY REV. J. MILNE CURRAN, P.G.S. 235 



Sometliing like what I have been supposing has actually taken 

 place in the past, with this diSerence that instead of one old 

 river bed under the plains, at one particular level, we have many 

 and on different horizons, from the fact that the formation of the 

 plains extended over great periods of time. 



The permanance of drainage-lines is one of the most remarkable 

 facts in the geological history of continents, and Australia is in no 

 way exceptional in this regard. The erosive action of the 

 western rivers and the forming of the plains may have been at 

 work long before Miocene times, when the whole southern portion 

 of the continent was upraised some 600 feet. At that time — in 

 the hey-day of its youth — the average fall of the Macquarie was 

 much greater than at present, and may be represented by a — 6 

 (Diagram I.) As the plains were formed the river occupied levels 

 as c, c^, e, while at the a level would be unaltered or eroded if any- 

 thing. An important point to note is that the newer beds all 

 branch from thei old ones, as in the case supposed above, and with 

 like results, namely that while some water will flow along the new 

 channel, a great deal will still get away by the old bed. 



It may be objected that if the plains were formed in the way I 

 explain, we should have not many old river beds at different 

 levels, but one great bed of river drift that has been slowly raised 

 while the plains were formed. We might, I admit, expect some- 

 thing like this, if the rivers deposited alluvium to an equal depth, 

 and at the same time over the whole surface of the growing and 

 gradually spreading plains. Then the river would not leave its 

 channel, as when the latter was raised, the banks and surrounding 

 country would be raised to an equal extent. It is almost needless 

 to remark that this is not at all in keeping with our knowledge of 

 the way rivers work in forming plains and depositing alluvium. 

 The great bulk of the transported matter is deposited on or near 

 the banks, so that in time the river margins and eventually the 

 river, will be above the level of the surrounding country. The 

 effect of this, in the end, is to alter the course of the river, only 

 , to begin again the same cycle of change. Thus, during the 

 formation of the plains, we have old river beds, (connected with 



