Contents, ix 



CHAPTER VI. 



TEACHYTB AND BASALT. — DISTRIBUTION OF VOLCANIC ISLES. 



The sinking of crystals in fluid lava — Specific gravity of the consti- 

 tuent parts of trachyte and of basalt, and their consequent 

 separation — Obsidian — Apparent non- separation of the elements 

 of plutonic rocks — Origin of trap-dikes in the plutonic series — 

 Distribution of volcanic islands ; their prevalence in the great 

 oceans — They are generally arranged in lines — The central 

 volcanos of Von Buch doubtful — Volcanic islands bordering con- 

 tinents — Antiquity of volcanic islands, and their elevation in 

 mass — Eruptions on parallel lines of fissure within the same 

 geological period . . . . . . . PAGE 132 



CHAPTER VII. 



AUSTRALIA; NEW ZEALAND; CAPE OP GOOD HOPE. 



New South Wales — Sandstone formation — Embedded pseudo-frag- 

 ments of shale — Stratification — Current- cleavage — Great valleys 

 — Van Diemen's Land — Palaeozoic formation — Newer formation 

 with volcanic rocks — Travertin with leaves of extinct plants — 

 Elevation of the land — New Zealand — King George's Sound — 

 Superficial ferruginous beds — Superficial calcareous deposits, 

 with casts of branches ; its origin from drifted particles of shells 

 and corals — their extent — Cape of Good Hope — Junction of the 

 granite and clay-slate — Sandstone formation . . . 146 



APPENDIX TO PART I. 



DESCRIPTION OP FOSSIL SHELLS, BY G. B. SOWERBY, ESQ., F.L.S. 



From a Tertiary deposit at St. Jago, in the Cape de Verde 



Archipelago 171 



Extinct land-shells from St. Helena 173 



Shells from the Palaeozoic formation of Van Diemen's Land . 176 

 Description of Fossil Corals from the Palaeozoic formation of 



Van Diemen's Land, by W. Lonsdale, Esq., F.G.S. . . 178 



