president's address. 609 



•earth deposit was examined at Bugaldi, and was seen to be over- 

 lying as well as capped by basalt. 



The most interesting results of the trip were, however, the 

 physiographical. The volcanic masses are, in Mr. Jensen's 

 opinion, the remains of an old dome-shaped lava plain, to which 

 the term " conoplain " may be extended to apply. The dissection 

 of this plain has taken place mainly through " arid agencies." 

 We have then, in this district, excellent examples of "arid 

 erosion." 



Before returning to Sydney Mr. Jensen visited the Nandhewar 

 Mts., which, both in petrological character and in topography, 

 bear close resemblance to the Warrumbungles, and also give 

 definite evidence of the arid cycle type of erosion. 



On his return from this expedition in December, the Macleay 

 Fellow took up the chemical investigation of the Glass House 

 Mountain rocks, and has since made twelve complete rock analyses 

 and several silica estimations, which are bringing to light impor- 

 tant facts. Many of the rocks hitherto described as " orthophyric 

 trachytes " are, in reality, too acidic to bear the name of trachyte. 

 They belong to the comendites and pantellarites. The highly sodic 

 nature of all the rocks of the district was chemically veritied, 

 And the close relationship of the Pt. Arkwright porphyrite with 

 the Noosa Head quartz diorite was verified analytically as well as 

 mineralogically. 



During the past year, the Macleay Bacteriologist continued 

 ■certain work upon the bacterial origin of the vegetable gums. 

 The gumm}'^ exudate issuing from a species of Hakea was 

 shown to possess rather indefinite characters which militated 

 against tracing it to any of the bacteria that were found in the 

 tissues of the plant. The investigation, however, went far to 

 prepare the way for another research. While it is evident that 

 a gum or mucilage which may exude from a plant is abnormal 

 and may be the result of the work of micro-organisms, we are not 

 so ready to believe that a mucilage which does not exude and 

 which is a normal constituent of a plant, can have other than a 

 vegetable origin. Yet it has not been shown that a regulated 



