ARID PORTIONS OF SOUTH AUSTRALIA. 65 



there is a large amount of sand, some of fine grain and easily shifting 

 with the wind. For this reason one finds fences covered with sand 

 drift and sandy hillocks. There are also a few moving dunes of small 

 size. In the low hills the soil appears to be all or part clay, or at least 

 of very fine structure, as a sandy loam. There is evidently very little 

 humus. So far as the depth of the soil is concerned it can be said to 

 vary greatly. On the plain near Copley it is 4 meters or more. Among 

 the hills, on the other hand, there are many areas where the rock is 

 barely covered with soil, and of course there are many outcrops in 

 which soil is entirely wanting. In any region, such, for example, as 

 that about Copley, where a small rainfall is a prominent environmental 

 factor of plants, the nature of the soil, including its depth, is of very 

 great importance in shaping the character of the plant covering as 

 well as its distribution. This fact is largely based on the circumstance 

 that the soil constitutes the sole reservoir for the reception and storage 

 of water. 



Owing to the broken topography the water-courses of the region are 

 not only numerous but also in many regards extremely varied. In 

 some the gradient is marked, in others it is relatively slight. The 

 channels may be very well developed and hence considerably below 

 the adjoining plain, or slope, as the case may be, or the converse may 

 be true. The leading drainage channels of all sorts are contributory to 

 Leigh's Creek. This stream, dry much of the year, takes its origin a 

 few miles to the east of Copley in the Flinders Ranges, and running 

 northward it joins the Fromme River and ultimately discharges into 

 Lake Eyre. To the south of Copley, and a little beyond the region 

 studied, the streams run in the opposite direction and into or toward 

 Lake Torrens. Although the drainage is generally very well defined, 

 there are relatively small separated basins, mainly on the Copley 

 plain, which have inadequate drainage or no surface outlet. In such 

 depressions there is a large accumulation of salts. 



It will be seen from the above sketch that the leading physiographic 

 divisions or units can be said to be the hills, the Copley Plain, and the 

 washes. For convenience, the hills will be divided into (1) the Mount 

 Deception Range, such of the Flinders Ranges as lie to the west of 

 Copley, and (2) Table Mountain and Mount of Light, with the nearby 

 hills, to the east. For the purpose of further distinguishing the locali- 

 ties to be referred to below, they will be mentioned in reference to the 

 roads which lead to them, as follows : 



North of town: Myrtle Springs road crosses the plain northwest of the 

 village, goes through the low hills to the east of the Mount Deception 

 Range, and finally through that range. Yudnamutana road goes north 

 and northeast of town, passes along the western side of the Flinders 

 Ranges, and at length penetrates them; this road also crosses the plain 

 and runs over low hills, where it passes out of the Copley vicinity. 



