ALKALINE ROCKS. l9l 



and more directly by the great abundance of liquid and gaseous 

 inclusions in the adularia felspar which comprises the greater 

 part of the rock. The fabric of this rock in the major part of 

 the outcrop is typical of entectic crystallisation. Besides a little 

 quartz and a predominance of adularia, the constituents include 

 some sphene and rather abundant tourmaline ; the latter often 

 in graphic intergrowths. 



The south-east margin of the pre- Cambrian area, where 

 examined on Arkaroola Creek, is flanked by a coarse breccia con- 

 sisting chiefly of boulders and angular masses of the adjacent 

 pre-Cambrian quartzite. 



In both the locaUties described there is a marked difference 

 in the vegetation and topography of the Cambrian and pre- 

 Cambrian areas. The latter are much more rugged and the out- 

 crops more rocky. These rocky hills support abundant scrubby 

 vegetation, such as acacia and mulga ; even mallee and pine trees 

 are met with on the more elevated ground. 



The low undulating hills and plains country, more typical of 

 the Cambrian areas, support abundant herbage and salt bush ; 

 whilst scrub growth is less conspicuous. 



EXPLANATION OF PLATE XV. 



Figs. 1 and 2 of plate are illustrations of the typical appearance 

 of Cambrian as distinct from pre-Cambrian outcrops in the Yudnamutana 

 district. In the former the absence of vegetation is not truly natural, being 

 the outcome of long-continued overstocking and the rabbit pest. 



REPORTS OF THE RESEARCH COMMITTEES. 



On {a) Alkaline Rocks ; (6) Glacial Phenomena ; 

 (c) Structural Features of New Zealand. 



ALKALINE ROCKS OF AUSTRALIA. 



Resolutions carried, Brisbane, 1909 : — 



{a) That a Committee of the Geology and Mineralogy section 

 be appointed to investigate the alkaline rocks of Australasia, 

 consisting of Professors David and Marshall, Dr. H. I. Jensen 

 and Professor Skeats (Dr. Jensen, Secretary). 



{b) That a sum of £50 be set aside for the further investiga- 

 tion into the nature and origin of the alkaline rocks of Australia. 



