101 



quite flat upon the ground, and the foliage, which is confined to the terminal 

 branches, is spread as a bushy carpet. 



The presence of three peaks — 600 feet high or over — upon North 

 Island causes raincloud or mist to hang about the higher levels to a considerable 

 degree. Thus, on the morning of our landing there was light rain about 6 a.m., 

 and the peaks were blotted out by clouds. These gradually lifted as the sun rose, 

 but they hung about the top 200 feet or so of 781 Hill until nearly 11 a.m. In 

 winter this cloud efifect must be considerable. The ground flora at and just 

 below the summit of 781 Hill includes several mosses, and the fern Cheilanthes 

 teniiifolia suggesting a greater humidity than lower down the slopes or even along 

 the water courses. 



The insolation factor upon the islands must be very severe, and aspect dififer- 

 ences between north or west slopes and south or east are marked. The two 

 former are much drier and the rock weathers more rapidly than in the case of the 

 latter. This is particularly well seen in the case of East Hill when viewed from 

 the col connecting it with 781 Hill (pi. iv., fig. 1). The north face has 

 precipitous granite tors and rocky slopes supporting an open flora of shrubs ; 

 this extends almost to the summit. On the south face the angle of the slope is 

 lower with less bare rock. Casiiariua woodland, which is the climax com- 

 munity on hill summits, extends down the slope for some distance on the south 

 side, and when it passes into scrub communities the latter are thicker and less 

 open. 



II. Edaphic. 



In Appendix I. Mr. J. G. Wood gives the results of certain analyses made 

 of soil samples collected upon the islands. There are three soil types on the 

 Pearsons — blown sand, travertine, and granitic. 



The first, as described above, is limited to a small patch at the south end 

 of Middle Island near the landing place. It need not be considered further. 



The travertine soils consist of a coarse granitic sand mingled with particles 

 of limestone of all sizes from small fragments to large blocks several square 

 feet in area. The soil appears to dry out very thoroughly ; in January there 

 was no cohesiveness between the particles at a depth of 8 to 9 inches. Below 

 this depth large travei'tine masses form the main deposit. The sample of 

 travertine soil analysed was collected from the middle of Southern Island. The 

 analysis ( Sample 1 ) shows that there is 6 per cent, humus, 97 per cent, calcium 

 carbonate. -38 per cent, nitrogen, -79 per cent, sodium chloride. It was dis- 

 tinctly alkaline pH=8. 



The granitic soils range from talus and rubble to coarse sands. The water- 

 retaining capacity of such soils is low, and the rain that falls upon them would 

 rapidly percolate to the solid rock below. These soils are invariably dry and 

 powdery to the touch. The samples felt ''air dry" at the time they were col- 

 lected. Five samples were taken, one in each of the two main communities — 

 Atriplex, "saltbush," plain (Sample 2), Casiiarina woodland (Sample 3) — and 

 three in Main Creek, at the head and in the upper part, to test the range of 

 salinity in the soil (Samples 4, 5, and 6). 



Samples 2 and 3 show a general similarity. The Casuarina woodland has, 

 a? might be expected, the higher humus content, 13-9 per cent., as against 

 99 per cent, in the saltbush soil. Both soils have only average salinity (-20 per 

 cent., 23 per cent.). The most striking difference is in the pH values. The 

 woodland soil has an acid reaction pH=6; the saltbush plain is somewhat 

 alkaline. pH=74. 



Sample 4 is typical of much of the poorer soil on well-drained slopes. 

 Such soils are poor in humus and soluble salts. Samples 5 and 6 were taken 

 respectively at the edge of and within one of the granite basins that occur at 



