156 president's address — section c. 



Reserve No. 23, certain plant remains were found in a deposit con- 

 taining what is evidently the detritus of the lateritic beds. These 

 plant remains have, on examination, been held to belong to the Euca- 

 lypti. McCoy has described definite eucalyptus foliage from the older 

 gold drifts in Victoria, whilst Ettinghausen describes several species 

 from the Upper Tertiaries of New South Wales and deep lead in the 

 New England tinfield. 



On this evidence, therefore, the laterites seem to be of earlier age 

 than Late Tertiary, though there is but little doubt that laterite deposits 

 are forming at the present time. 



(c) The Volcanic Rocks. — Volcanic rocks have played an important 

 part in the geological history of Western Australia, and the evidences 

 of this igneous activity are to be found in the form of lava-flows, ash- 

 beds, breccias, dykes, sills, &c., which make a prominent feature in 

 certain portions of the State. 



Many writers and observers, it must be noted with regret, treat 

 volcanic rocks in such a fashion as to suggest that they constitute a 

 more or less meaningless interpolation in geological history, and I 

 have no desire to be included in the same category. 



There are, so far as is at present known, three distinct periods in 

 which Western Australia has been the scene of igneous activity of 

 more or less intensity. These periods are : — 



(a) In Pre-Cambrian time, prior to the deposition of the beds 

 containing the Olenellus fauna. These old igneous rocks 

 are of importance in the part they appear to have played 

 in connection with the formation of the ore deposits of 

 the State. These have been more or less fully described 

 in the opening portions of this address. 



(6) A period commencing early in Nullagine (Devonian) time, 

 but ceasing before the Carboniferous. The interstrati- 

 fication of lavas and ashes with the sandstones and con- 

 glomerates point to subaqueous eruptions, though from 

 the amygdaloidal nature of many of the lavas the bulk 

 of these volcanic rocks must, I think, be sub-aerial. 

 Several of the focii from which the lavas, &c., emanated 

 have been noticed. The magnificent series of basic 

 dykes of the north-west and elsewhere, to which reference 

 has already been made, suggest to one who has examined 

 the Devonian volcanic series that fissure eruptions, of 

 which these dykes may form part, have been in some 

 way responsible for the wide extent of the lava flows — 

 which cover some hundreds of square miles. 



(c) After the deposition of the Jurassic beds, and believed to 

 be of Tertiary Age. They consist of basic lavas and ashes, 

 which occur in great force in the Kimberley district. 



In the Ord and Bow valleys there lavas appear to have levelled 

 up the depressions formed therein (except certain knife-edge ridges 

 of the older rocks, which still protrude above the level), and in places 



