113 



Little need be said regarding" the moisture at 100° C. This is low, as would 

 be expected of coarse sands, and the range is small between the different samples. 

 The water-retaining-capacity factor alone appears to influence the plant dis- 

 tribution very slightly. The highest percentage of water is reached in the case 

 of soil No. 6, obtained from the basin at the head of the creek. It contains 

 more clay than the other soils, the felspar being largely kaolinized. 



The presence of clay (hydrous silicate of alumina) is reflected also in the 

 second column (combined water). Rough estimations showed that the combined 

 water was practically nil in all cases except in soil No. 6, where it was deter- 

 m.ined. It amounted to 3 per cent. 



The column headed "humus" was determined by the loss on ignition after 

 deducting the CO.. and the total water content, which gives approximately the per- 

 centage of humus. This is complicated in the case of soils Nos. 1 and 2 by the 

 fact that a good deal of dried undecomposed plant debris (twigs and portions 

 of roots) passed through the sieve. To determine these the soils were shaken 

 with water, when most of the small twigs floated to the top. These were 

 collected and dried, and were found to amount to about 3 per cent, in each case. 

 They do not, however, alter the relative positions of the soils in regard to humus 

 content. Soil No. 3 is a dark soil from the Casuarina woodland zone containing 

 139 per cent, of humus and comparatively free from small twigs.. As one 

 usually finds in woodland soils, it contains an acid humus, as is shown in the 

 pH value in the last column in the table. This soil forms a notable contrast 

 with soil No. 2, with which it is practically identical in composition, except 

 that the humus content is about 4 per cent, lower in No. 2 (taking the twigs into 

 account ) . 



No. 2 soil is not acid, however, but on the alkaline side of neutrality 

 (neutrality pH=70). It appears possible that the reaction of the soil 

 may be one of the factors influencing the type of flora, for whilst the acid soil 

 supports Casuarina and Leucopogon, the alkaline one is covered with Atriplex. 

 In soil No. 5 the organic matter is well decomposed and contains no twigs. 

 It approximates soil No. 2 in composition, though it is poorer in humus. Soil 

 No. 4 is very deficient in organic matter. It is a typical barren granitic soil. 



The fourth column gives the percentage of chlorine, and the next these 

 percentages calculated as sodium chloride. There is practically no K CI present, 

 the potassium which is present being combined with aluminium silicate in the 

 clay. A determination of the total soluble salts in soil No. 6 showed that these 

 amounted to 34 per cent., and of this 308 per cent, was Na CI, as calculated 

 from the chlorine content. There was very little potassium present. The salt 

 is derived from sea spray, and the analyses show that two soils, Nos. 1 and 6. 

 have abnormally high percentages. 



The most interesting feature brought out in connection with the salt con- 

 tent is the range of Atriplex, which is usually classed as a halophyte. In Nos. 2 

 and 5, with an average soil saline content, A. pahidosuni thrives, while A. 

 cmerciim tolerates 097 Na CI. In soil No. 6, where the salt content is high 

 (due to accumulation by evaporation of sea water in the basin), Atriplex is 

 absent. The characteristic vegetation is Arthrocnemuin halocncmoides, var. 

 pergranulatimi, and Melaleuca halmaturorwm. 



The presence of Atriplex spp. in the areas of low salt concentration, and 

 their absence from soils with a high percentage of sodium chloride, supports 

 the objection that has been made to classing the "saltbushes" of Australia as 

 halophytes.'^^-^ 



The carbonate content calls for no comment here ; calcium carbonate is 

 present only in the soil from the travertine plateau. 



C12) Adamson and Osborn, Trans. Roy. Soc. S. Austr., xlvi. (1922), p. 544. 



