PRESIDENTIAL ADDRESS. 



found in the fact that the continuity of the newest diabase 

 dykes, which cross the field in a direction about north-east 

 and south-west, is very materially affected. Many of the 

 rocks are sheared, and the quartz reefs folded and over- 

 thrust, all of which points to this being a region of great 

 dynamic movement. 



"3. The Warrawoona belt extends northwards fifteen 

 miles to Marble Bar, which field is also traversed by at 

 least four major faults, which have a general northerly 

 strike. These faults have played great havoc with the 

 newer diabase dykes, as may be seen by an inspection of 

 the geological map (pi. 14, Bull. 40). Of the age of the 

 faulting both here and at Warrawoona, there is no direct 

 evidence, other than that it is younger than that of the 

 newest diabase dykes, of whatever age they may be. 



" 4. The Collie Coal Field is bounded by two faults trend- 

 ing generally north-west and south-east. The faults are 

 of considerable horizontal extent as well as of great down- 

 throw. I am rather inclined to regard the boundaries of 

 the great Stirling Range, as marking the extension of the 

 Collie group of faults." 



The trend and positions of these lines of faults are shown 

 on Plate 2, and the rift valley and the folds in the adjacent 

 peneplain are shown in figure 1. 



Fig. I. Diagrammatic Section across the great trough fault of West Australia. 



from daia suggested by A Gibb-Maitland F.G.S. Vertical Scale B.OQO feet fo an inch. 



-/ n Darlinq Range 



Fremanlle Perfh 



1 schistwv 



N- \ \ 



& GNEISS1C r-| 

 \ v X 

 s GRANITE 



-50 miles 



Penh 



Geraldfon Dongara Fl G. 2. LONGITUDINAL SECTION OF AB ; 0VE 



. &6NEISSIC 

 \ \ V\ 



«, 'GRANITES 



Bunbury 



fcsalr 



Verncal Scale 20.000 Peer to an inch 



