ON THE GEOLOGY OF WEST MORETON, QUEENSLAND. 155 



Pitchstone, Spicer's Gap. — A nearly colourless glass, 

 crowded with minute microlites of felspar in the form of 

 excessively thin idiomorphic plates. Sometimes these are 

 arranged one above the other in sets of three, with the 

 axes of the three plates inclined to one another. At other 

 times they have a kind of echelon formation. These over- 

 laps give the appearance of twinning but the plates are 

 really simple. 



There are a very few larger phenocrysts of sanidine, 

 idiomorphic and twinned after the Oarlsbad law and some- 

 what corroded by the base. 



Olivine-basalt, near the summit of Mount Mitchell. — The 

 base is pilotaxitic with a very marked flow structure. It 

 consists of plagioclase, augite, magnetite, ilmenite, and 

 apatite. 



The plagioclase is labradorite (Ab 9 Ann) in lath shaped 

 crystals up to 0*5 mm. in length, twinned after Oarlsbad 

 and albite laws. 



Augite is purplish and faintly pleochroic from brown to 

 purple and is ophitically arranged. 



Magnetite in small octahedra and ilmenite in thin plates 

 appear to be quite independent of one another. There is a 

 good deal of dark green chlorite throughout the slide, also 

 large quantities of apatite in very fine needles. 



Olivine is fairly abundant in idiomorphic crystals up to 

 1 mm. by 0*5 mm., much altered to dark green fibrous 

 serpentine. A few irregular cavities are filled with analcite. 



Coarse olivine-basalt, South-east corner of Portion 121, 

 Parish Clumber (near the baseofMoitntMitchell. — Coarsely 

 pilotaxitic in structure. Two generations of plagioclase 

 are present. The individuals of the first set are large 

 prismatic crystals with square cross sections and reach 

 4 mm. by 0*5 mm. They consist of labradorite Ab 3 An 4 and 



