ARID PORTIONS OF SOUTH AUSTRALIA. 83 



the well-known Ooldea "soak," which has played an important part 

 in the activities of men of all sorts who have been in these parts. 

 Here, in a sandy depression, is to be found a fairly good supply of 

 potable water which appears to be the only water of its kind for a 

 very great distance. Explorers have relied on it for their supply, the 

 aborgines come to it frcm long distances in the course of their wander- 

 ings, and it has been an important factor in the construction of the 

 railway, providing good water for camps. 



The origin of the sand on the NuUarbor Plain and of the sandhills 

 appears not to be surely known. So far as the sand on the plain in 

 the vicinity of the sandhills is concerned it may have been moved 

 there by wind action from the east, as is popularly supposed. Another 

 hypothesis is to the effect that the Nullarbor Plain was laid down not 

 far from shore and hence that it had a large admixture of coarse 

 material, which was set free upon the elevation and the subsequent 

 erosion of the plain. So far as the origin of the sand in the sandhill 

 region proper is concerned, Howchin (1909:67) suggests that it may 

 have been derived from the "waste of the granitic rocks, which form 

 the bedrock of the country." The same author says also that the 

 calcareous material, which was derived from "breaking down and 

 solution of Kainozoic limestone, has cemented the sand, in places, 

 into calcareous sandrock, or has laid down from solution a crust of 

 calcareous limestone." Possibly the calcareous core of the sandhills, 

 above noted, had some such origin. 



The sandy soil in the Ooldea vicinity is fairly coarse and permits the 

 rapid absorption of water. If, for example, a bucket of water is 

 emptied quickly on level ground it spreads only slightly beyond the 

 place where it is poured and sinks from sight almost immediately. 

 This being the case, it would be expected that water derived from the 

 rains would also sink quickly and without appreciable run-off. Such a 

 condition was observed at the time of a storm of September 14. On 

 this day there fell, between 1 and 4 p. m., 0.21 inch of rain. At 

 4'' 15° p. m. the soil was moist to a depth of 3.5 cm. No rain occurred 

 during the night, but on the following morning the soil was found to be 

 moist to a depth of 9.5 cm. Apparently no run-off had taken place. 

 From these observations, and from the absence of all indications of 

 washing from storms, it is concluded that such water as falls on the 

 sandy soil at Ooldea is absorbed at once, and further, from the nature 

 of the soil itself, that it is well conserved. These conditions must be 

 taken into account when possible reasons for the relatively heavy 

 vegetation of the sandhill region are being sought. 



Climate. 



Ooldea is within the 10-inch isohyet. It is in the region of winter 

 rains, but apparently more or less precipitation is to be expected in 

 summer as well. It will be of great interest, in view of the fairly abun- 



