132 president's address — section c. 



After due consideration, therefore, I have chosen to invite your 

 attention for an academic hour to a succinct account of the recent 

 advances in our knowledge of the geology of the western portion of 

 this continent, to the investigation of which my attention has been 

 more immediately directed during the last decade. 



In a broad and general way the geology of "Western Australia 

 offers many interesting points of analogy with that of South Africa 

 and India. 



In the present condition of our knowledge of the geology of the 

 State it is almost impossible to deal systematically with the various 

 formations as a whole, for, owing to a variety of causes, geological 

 inquiry up to the present has consisted merely of a series of uncon- 

 nected observations, to the co-ordination of which we must look to 

 the future ; nevertheless, our observations have been so widely ex- 

 tended as to permit of certain broad generalisations. 



Geologically the rocks of the State may, for the purpose of this 

 address, be divided into three distinct groups, viz. : — 



(a) The Trystalline, Schistose, and Metamorphic Rocks, a group, 

 the members of which have certain features in common, 

 occupy definite areas, and various lines of inquir}'- point 

 to being of considerable geological antiquity, possibly 

 of Archpean Age, though, in the present condition of our 

 knowledge, I prefer to adopt the safer term — Pre-Cambrian ; 

 (&) The Sedimentary Rocks, which extend, with many blanks, 



from the Lower Cambrian to the most Recent; and 

 (c) The Volcanic Rocks, which are so largely developed in the 

 northern portion of this State, 

 (a) The Crystalline Schists and the Metamorphic Rocks. — The Pre- 

 Cambrian crystalline schists and metamorphic rocks constitute the 

 principal mineral region of Western Australia, and, so far as is at 

 present known, the area occupied by these venerable beds is about 

 two-thirds of the total superficial extent of the State, which is 975,920 

 square miles. As our knowledge advances, however, this estimate of 

 the area occupied by the Pre-Cambrian rocks may be subject to some 

 modification. 



There are probably few parts of this continent which can boast 

 of a finer development of these older rocks than Western Australia, 

 and perhaps no more promising field can be found for their investiga- 

 tion. 



Considerable interest in connection with these rocks centres — 

 so far as petrographical questions are concerned — in the transmuta- 

 tion of both the igneous and sedimentary formations into crystalline 

 schists. Observations in the field point to the possibility of the 

 mechanical movements to which the rocks have been subjected having 

 modified or obliterated structural features previously impressed upon 

 them, and that they may contain formation belonging to different 

 geological systems. Sections in the NuUagine district show these beds 

 to be made up of cleaved conglomerates, some of whose pebbles con- 

 sist of a pre-existing conglomerate from an earlier series of which no 



