548 president's address. 



I. Arch^an. 



In Australia and Tasmania rocks have been discovered of Pre 

 Cambrian (Archtean) Age, as old therefore, perhaps, as any rocks 

 known in any part of the world. 



In New Zealand Archaean rocks are doubtfully represented. It 

 does not, of course, follow that the areas now occupied by these 

 rocks are absolutely the oldest portions of the Australian Conti- 

 nent ; they are, however, absolutely the oldest known to us. 



In South Australia this group is developed (1) on a large scale 

 on either side of St. Vincent's Gulf near Adelaide, and forms the 

 basis of the Mt. Lofty Range. 



The rocks consist of gneiss, mica schist, slates, and reddish-purple 

 jointed micaceous shales. 



Professor Tate informs me by letter that there is a conglomerate 

 of gneissic pebbles in mica schist six to ten feet thick on the north 

 coast of Kangaroo Island and elsewhere. He also states that 

 graphite occurs in the Archaean rocks of the St. Vincent's Gulf 

 area, and that ilmenite forms a constituent of the gneiss at Hack's 

 Bridge, between Adelaide and Strathalbyn. 



The rocks are in places remarkably free from alteration, not- 

 withstanding their immense antiquity. It is these rocks which 

 have been powerfully glaciated at some unknown period of 

 geological time, as described by Professor Tate, of Adelaide 

 University."^ f :|: 



Their general strike is N.E. and S.W., the dip being chiefly to 

 S.E. at high angles, but reverse dips occur in places. 



At Mt. Lofty Mr. Brown states§ that their dip is chiefly south- 

 easterly for a distance of twenty miles. 



The steeper sides of the folds face the S.E., in which direction 

 they are bounded by a mass of granite evidently of considerable 

 extent, though hidden for the most part under Tertiary limestones. 

 At Ardrossan there is an immense unconformability between these 



* Trans. Roy. Soc. S. Australia, Vol. ii. p. 64. 

 + Ibid. Vol. viii. p. 49, 1886. 

 + Aust. Assoc. Adv. of Science, Vol. i. p. 231. Sydney, 1887. 

 §S.A. Ann. Rep. of Govt. Geologist, 1882-83. Adelaide, 1884. p. 10. 



