14 HORN EXPEDITION — PHYSICAL GEOGKAPHY. 



feet pel' mile. Between the Mission Station and the junction of the Palmer with 

 the Finke the rate of fall is five feet per mile, the difference in the altitude of the 

 two places being G99 feet, and the distance between them 135 miles. Lastly, the 

 (liH'erence in the altitudes of the Finke Channel at' the Palmer junction and at 

 Lake Eyre, a distance of 536 miles, is 980 feet, which gives a mean rate of fall of 

 less than two feet per mile. Between Heavitree Gap (1713 feet above sea level) 

 and Oodnadatta (397 feet above sea level), a total distance in a direct line of 357 

 miles, the fall of the slope of the surface averages about 3 '7 feet per mile. 



The above figures show, as might ha\e been expected, that the rate of fall is 

 at its maximum in the JNIcDonnell Ranges, and at a mininmm on the Cretaceous 

 plains near Lake Eyre, between which places there is a gradual decrease in the 

 rate of fall as we go from north to south. 



((-•) Nature of the Course and C/iaiiiiel of the Finke. — As one might expect, 

 judging froni the figures just given, the course of the Finke from the McDonnell 

 Uanges to the .southern slope of the James Range is not so sinuous as it is after 

 it debouches upon the Cretaceous plains. On these plains its course becomes 

 extremely meandering, the river making its way down the very gentle incline 

 from these ranges to Lake Eyre only after performing numerous sweeping curves. 

 The width of its channel varies considerably, being usually narrower and deeper 

 in the ranges, but widcuiing out as it leaves them. On emerging on to the plains 

 it becomes Hatter and shallower and dotted with gum trees, which are not confined 

 to the banks only as in the ranges, but grow often in patches even in the middle 

 of the channel. 



{d) Absence of Surface Running Water. — The absolute dependence of the 

 presence of running water in the bed i>f the Finke upon direct supplies of rain has 

 its explanation in the following facts : — 



(1) The basin of the Finke, although of great extent, is entirely confined, or 

 nearly so, to an area over which the climatic conditions are the same. 



(2) Rain falls usually only at certain seasons, there being long intervals of 

 drought. 



(3) There is an almost total absence of springs at the head of the Finke and 

 its tributaries, ajid in the few instances of their occurrence the discharge is very 

 small. 



The influence of tliese three factors on the absence of surface running water 

 is olnious. After the flood waters caused by a heavy downpour have subsided, 



