391 



as a great plain rising gradually to an eastern extension of the Central South 

 Australian highlands, which serves as the watershed between the Murray River 

 and the inland drainage to Lake Frome. These highlands are of comparatively 

 recent formation, geologically speaking, though composed of Cambrian rocks. ^^'^^ 

 The ancient river systems have been cut across by the uplift forming these 

 highlands, the altitude of which does not exceed 2,000 feet. Northward the 

 land gradually falls again to Lake Frome. Much of the highlands have under- 

 gone peneplaination, and consist of wide flat valleys between low hills. 



The rivers of the district are ill-defined and erratic in their direction of 

 flow. They are mere watercourses running only at intervals in times of flood. 

 They may be dry for years together and then come down in flood, overflowing 

 their banks and temporarily submerging the surrounding country for as much 

 as a mile or more on each side of the channel. Such watercourses have fre- 

 quently no opening to the Murray or to Lake Frome, but terminate on a flood 

 plain in a lake or swamp. Lake Frome itself is only a large example of this 

 type. These centres of inland drainage serve as evaporating pans and 

 accumulate a high percentage of soluble salts (see table of analyses). 



Climate. 



Rainfall. — The area lies wholly within the 10-inch isohyet. The rainfall 

 records of Florieton, near Dilkera Murray Basin, Koonamore, and Curnamona 

 are given below : — 



Mean Monthly Rainfall in inches. 



Period 

 locality of Jan. Feb. Mar, Apl. May June July Aug. Sept, Oct, Nov. Dec 



Mean 



for 

 Year 



Average 

 Annual 



Years 



Florieton 27 '49 '12 -59 '74 -89 1-11 -74 l-Ol -97 1-03 -64 70 9-43 9-97 



Koonamore 27 -70 '45 -61 -64 -93 1'08 '46 -63 '58 -81 -64 -59 8-18 8-46 



Curnamona 30 -62 -27 -48 '60 -88 -85 "33 -54 -49 '55 -55 "69 6-85 7-03 



These results are shown graphically in fig. 2. Mean figures may be 

 misleading, because in any single year there may be rainless or almost rainless 

 months, while in others, of course, the fall may be considerably more than 

 the mean. This applies especially to the northern stations. 



KOONflnOREg 



CURNWlONAl 



1-0 in. 



•5 in. 



Jan. Feb. Mar. Apl. Mav June July Aug. Sept. Oct. Nov. Dec. 



Text fig. 2. 



Diagram comparing the mean monthly rainfalls at Florieton 

 (River Murray Basin), Koonamore, and Curnamona. 



(11) Howchin, W., "The Evolution of the Physiographical Features of South Australia," 

 Rept. Austr. Ass. Adv. Sci., xiv., p. 148, 1914. 



