SOAJE GEOLOGICAL FEATURES OF NORTHERN AUSTRALIA. 115 



o': erosion and peneplanation. The earth fissures formed in the 

 pre-Cambrian and Cambrian movements have not been obliter- 

 ated by later folding. The problems to be studied in their 

 connection are chemical — those of leaching, secondary enrich- 

 ment, &c. 



Plateau Uplifts in General. — ^Platean topography is typical 

 of most of the tropical regions of the earth. Thus the Saharan 

 portion of Africa, the whole of Arabia, the Deccan in India, 

 Northern South America (Venezuela, Columbia, and Guiana) 

 and Northern Australia, geologically studied, are plateau 

 regions. Mostof the adjacent seas are Senkungsf elder. Perhaps 

 the earth's rotation on its axis has something to do with this 

 condition. In these regions (tropical regions) the trend lines, 

 or axial directions, of mountain ranges are predominantly 

 west-north-west in the southern hemisphere, and west-south- 

 west in the northern hemisphere, a feature which is even more 

 noticeable in comparing Palaeozoic strike directions than in the 

 study of Cordilleran axes . It is also significant that in temperate 

 zones the main axial directions are north-west in the southern 

 and north-east in the northern hemisphere. 



The data obtainable so far are somewhat crude and have 

 never been systematically collected with a view of pursuing 

 tliis study, but the facts laiown to us point to a plasticity of the 

 earth's crust in the Archean period, which caused the sub- 

 crustal igneous magmas to take on directions analogous to the 

 trade winds. If further studies can elicit more facts in con- 

 firmation of tliis rule, the planetesial hypothesis can be 

 definitely abandoned and the Lamarckian theory of the earth's 

 origin can be regarded as definitely proved. 



Blue and White Quartz. — In McLaren's ■ Gold " (The 

 Mining Journal, London) it is emphasised that the auriferous 

 Archaean terranes of Western Australia. Deccan, and South 

 Africa, are characterised by two kinds of quartz — an older blue 

 quartz and a later white quartz. This characteristic has also 

 been noticed in the pre-Cambrian of the Northern Territory. 

 The hornblendites and amphibolites which antedate the granitic 

 intrusions {see N. T. Bulletin No. 16, pp. 47 and 48) are 

 frequently traversed by veins of this blue quartz. Definite 

 evidence of the relative ages of the amphibolites and granites 

 was obtained by the writer in the Margaret and Pine Creek 



