192 HORN EXPEDITION — BOTANY. 



wliilst a few are recorded because of their rarity. Some of the species have 

 already been mentioned as occurring in the Larapintine area. 



The vegetation of this section of the country embraces that of the flood-ways 

 of the rivers and creeks, particularly the delta-like reticulation of the Stevenson 

 River north of Macumba, that of the sand-/ii//s and that of the gibber-fields. 



By far the richest ilora as regards numbers of species is that found along the 

 margins of the water-channels at their lower elevations ; here Eucalyptus micro- 

 tJieca, Acacia aneura, A. cyperophylla and A. hoiiialopliylla are conspicuous ; and in 

 favourable seasons a varied and luxuriant growth of grasses prevail. 



The sand-hills yield a considerable variety of annuals after copious rain, but 

 Triodia is rarely present and only as T. irritaiis (when accurate determination was 

 possible), but Spinifex paradoxus is common. 



However, the most prominent physiographic feature is that of the " gibber- 

 field.s," which are most characteristically exhibited from near Macumha to 

 Charlotte Waters. The gibber-fields which are, probably, of the same nature as 

 the "stony desert" of Sturt, are co-extensive with the area in which the outcropping 

 surfaces of Cretaceous beds have been altered to a hard splintery rock by infiltra- 

 tion or by substitution of chalcedonic or opaline quartz. Where this kind of rock 

 occurs, usunlly as a crown to tabular elevations, the surface around is thickly 

 strewn with its broken fi'agments, ranging from blocks of several cubic feet to 

 road-metal size, and graduating to smaller dimensions with increasing distance 

 from the source of supply ; among the stones and beneath them is a red loess. 

 At some points could be recognised the sources whence the gibbers had been shed, 

 whilst more extensively the original stores have been exhausted. At the times of 

 our tr.averses, the gibber-fields offered the most desolate aspect — the annuals had 

 disappeared and the shrubby vegetation had been reduced to the condition of 

 skeletons of dried branches and twigs ; though, from traces of herbaceous plants, 

 it may not be unreasonable to infer that after copious rains an ephemeral vegeta- 

 tion may be comparatively abundant, it can never be absolutely abundant because 

 of the very limited .space available by reason of the crowding of the gibbers. 



Here follows a list of the plants observed around Mount 8(iuire, twenty miles 

 north from Crown Point, the most nortlily extension of this type of country : — 



Lepidium papillosum Helipterum Fitzgibboni 



Frankenia laevis Helipterum Tietkensi 



Salsola kali Brachycome ciliaris 



