rock, but rather from the circumstances of finding there such 

 combination of physical conditions most favourable for its 

 growth and propagation. Hence, a species restricted in the 

 Ardrossan area to a granite may exist elsewhere on a rock of a 

 very different type, provided always it presents the surface 

 and sub-surface features of the granite. As instances of the 

 kind he mentioned that Casuarmes and Pittosporum pMltyrceoides 

 (ding to the quartzite bands in the Hundred of Munno Para, 

 though they are generally distributed about Ardrossan ; 

 Nicotiana suaveolens lives on the Silurian limestones only about 

 Ardrossan ; but farther south about Stansbury, it occurs only 

 on the seaward face of the Miocene cliffs. Local peculiarities 

 most certainly occur, but they are not of sufficient magnitude 

 to affect the aspects of the vegetation, which prevail over very 

 large tracts of land in this country. Though they give rise, in 

 some substances, to abnormal features ; thus Sal soli Kali, which 

 in Europe and throughout littoral Temperate Australia lives 

 only within the influence of the sea, is a characteristic plant in 

 the arid interior of this continent. Its presence there cannot 

 be explained on the supposition that it has survived the 

 geological changes which converted the interior from a sub- 

 marine area to a continental one. Other plants, such as 

 Salicomia arouscula or samphire, are similarly out of place. 

 The excessive variability of temperature and of the amount of 

 aqueous precipitation, as rain and dew, must in conjunction 

 with the hygrometrical properties of the soil determine to 

 a large extent those lines of demarcation which separate 

 extensive tracts of forest land from grass land regions, and 

 in other cases. In tropical countries this phenomenon is still 

 more marked, and the line of junction of absorbent and 

 retentive soils can be traced on the surface by the changes in 

 the botanical features. Perhaps in no other case is there such 

 an intimate association between plants and soil, as is shown by 

 the vegetation flourishing on the fluviatile Tertiaries, which 

 occur here and there from Cape Jervis Promontory to beyond 

 Nuriootpa. It did not escape the notice of Mr. Selwyn, who 

 writes : — " On crossing the bridge over the Onkaparinga at 

 Clarendon, and ascending the steep hill on the south bank of 

 the river, a sudden change takes place in the character of the 

 country, and the presence of Tertiary rocks is at once indicated 

 by the deep sandy soil, and thickly covered with epacris, 

 prickly acacia, dwarf banksia, coarse grass, and other scrubby 

 vegetation, so characteristic of sandy Tertiary deposits." The 

 vegetation is not so much peculiar as it is distinctive as a 

 whole. Other sandy patches occur which do not present the 

 same botanical f acies, and it must be evident that other circum- 

 stances determine the assemblage of the plants on these par- 



