1G6 PROCEEDINGS OF TPIE ROYAL SOCIETY OF QUEENSLAND. 



DESCRIPTION OF PLATE IV. 



This shows six mierophotographs of the anorthoclase basalt and 

 of the various basalts with which it has been compared. The first four 

 mierophotographs have been taken with crossed nicols, and tlie last 

 two in ordinary light. In all cases the magnification was 17 times. 



No. l.—AnortJioclasc Bayfilt from ]Mapleton, Blaekall Range. Micro- 

 slide No. 266. In the centre of the field there is a 

 phenocr3'st of anorthoclase showing simple twinning, 

 inclusions of augite granules, &c., and a clear zone 

 around the margin. The groundmass is composed of 

 plagioclase, augite, olivine, and magnetite. Crossed 

 nicols ; magnified 17 times. 



No. 2. — Anorthoclase Bafalt from Mapleton. This is another portion 

 of the same slide, as used for No. 1, and shows much the 

 same features. Crossed nicols; magnified 17 times. 



No. 'S. — Olivine Basalt, Mapleton Falls, Mapleton, Blaekall Range. 

 Microslide 260. This rock immediately underlies the 

 anorthoclase basalt. It contains phenocrysts of olivine 

 sot in a groundmass of plagioclase, augite, olivine, 

 magnetite, and a greenish glass. Crossed nicols; 

 magnified 17 times. 



No. 4. — Basalt from road cutting near State School, Montville, 

 Blaekall Range. Microslide 262. This slide is repre- 

 sentative of the basalts of Blaekall Range, and is 

 composed of plagioclase, augite showing ophitic struc- 

 ture, olivine, magnetite, ilmenite. and a greenish-brown 

 glass. Crossed nicols; magnified 17 times. 



A"o. 5. — Basalt from 3,000-ft. level. Eastern slope of Mt. Lindsay, 

 MacPherson Range. Microslide 221. Occasional lath- 

 shaped crystals of plagioclase occur in the hypohyaline 

 groundmass, which is streaked parallel to direction of 

 flow. Ordinary light; magnified 17 times. 



No. 6. — Oligoclase Basalt from Spicer's Peak, Main Range. Micro- 

 side 116. This slide shows the very fine-grained nature 

 of the rock. The dark patch in the centre represents a 

 crystal of olivine. Ordinary light; magnified 17 times. 



