b CONTENTS. 
Chapter IV — Continued. 
Quartz-porphyries— Continued. 
Microscopical description— Continued. 
Groundmass .-. 
. 41 
Accessory constituents * i 
Aporhyolites . 2 
Distribution , 9 
Macroscopical description 42 
Microscopical description 44 
Phenocrysts ,. 
Feldspar and quartz 44 
Other porphyritic constituents 45 
Groundmass 4g 
Fluidal structure 4g 
Micropoikilitic structure 47 
Spherulitic structure 51 
Chain spherulites 53 
Axiohtic structure 54 
Ehyolitic structure 54 
Lithophysal structure 55 
Micropegmatitic structure : 55 
Perlitic structure ... zx 
~ — — 00 
Amygdaloidal structure 55 
Taxitic structure 57 
Summary of proof of devitrification 57 
Opinions of petrographers , 59 
Chemical composition of the acid eruptives 61 
Acid volcanic breccia r o 
Distribution po 
™f "."""'.."::."".".".::.".:::"::".:::'.:::::::: 63 
r low breccias po 
Tuffaceous breccias n> 
Metamorphosed acid eruptives : sericite-schists and slates 64 
Summary fifi 
Chapter V. Petrographical description of the basic eruptives C8 
Nomenclature CQ 
bo 
Melaphyres and augite-porphyrites 69 
Distribution pq 
Macroscopical description 79 
Microscopical description 72 
Original structures 72 
Secondary structures 73 
Original constituents 73 
Secondary constituents 74 
Accessory minerals 77 
Discussion of chemical analyses 7g 
Basic slates 7 o 
Distribution and description 79 
Basic pyroclastics 80 
Distribution and description gg 
Crushed porphyrites gO 
Tuffaceous breccia gQ 
Ash «"™..™"™! 80 
Summary g.. 
