8 T. W. E. DAVID. 



of the islands of Rottnest and Houtmens Abrolhos possibly 

 mark the northward extension of these latter. The eastern 

 fault which forms the escarpment of the range brings the 

 palaeozoic and newer rocks in juxtaposition to the ancient 

 crystalline schists, which are believed to be of Archaean 

 Age. The sedimentary rocks which All this " rift valley " 

 are so arranged that there is a gradually ascending series 

 southwards from the Irwin River Coal Field. Cretaceous 

 rocks outcrop at Gin Gin, they have been met with in some 

 of the bores in the metropolitan area, beneath Perth, and 

 also rise to the surface to the southward along the coastal 

 plain. The most recent beds in this "" rift valley " make 

 their appearance near Bunbury, and are associated with 

 more or less horizontal sheets of basalt, these latter out- 

 crop at Bunbury, at several places in the bed of the Black- 

 wood and the south coast between Cape Leeuwin and Cape 

 D'Entrecasteaux, they have also been met with in a bore 

 put down in the valley of the Donnelly River. There 

 seem reasons for believing these to be contemporaneous 

 with the bedded basalts of South Australia and Victoria, 

 if so then it is very likely that this fault is Late or Post 

 Tertiary. 



" 2. On the Warrawoona Field, Pilbarra Gold Field, (Bull. 

 40, plate 10, of reprint of Bulls. 15, 20, and 23) a very 

 marked fault at least six miles in length, traverses the 

 held in a N.W. and S.E. direction, and probably extends far 

 beyond the limits of the area mapped. The fault hades to 

 the N.E. at about 60 degrees. A glance at the map shews 

 several bands of quartzite disposed somewhat in the 

 shape of a fan, the ribs of which open out gradually to the 

 west. The peculiar mode of occurrence, and ending off of 

 these beds is strongly suggestive of this line marking an 

 important fault, which, however, makes no show at all on 

 the surface. Further evidence of this hypothesis is to be 



