Igneous Roch 



EXPf.ANATION OF PLATES, 



Platk I. 



Fig. 1. — Microphotograph of a fractured garnet crystal occurring 

 in dacite from the Blacks' Spur. Inclusions of colourless 

 ■ quartz and black pyrrhotite are visible. Ordinar}- light, 

 X 14. 



Fig. 2. — Microphotograph of cherty ash, from a cutting in the 

 road, one-third of a mile above Wade's Look-out. Kude 

 bedding planes are visible in this section. Ordinary light 

 xl2. 



Fig. 3. — Microphotograph of a finely corroded, originally idio- 



morphic, quartz jjlienocryst, occurring in rh3'^olite, from 



the Acheron River above St. Fillans. Ordinary light 

 x31. 



Fig. 4. — Microphotograph of a cordierite trilling in dacite, from 

 near the head of the Acheron River. Crossed Nicols, 

 x50. 



Fig. 5. — Microphotograph of andesite, from the Don road, 2 miles 

 north of Launching Place. Ordinary light x 25. 



Fig. 6. — Microphotograph of porphyritic rhyolite, from Archer's 

 Look-out, Narbethong. Flow structure around an idio- 

 morphic phenocryst of quartz is well seen. Ordinary 

 light X 25. 



