Pattinson, Mr., on the separation of lead and silver.

Paul's, St., rocks of.

Pearlstone.

Peperino.

Peron, M., on calcareous rocks of Australia.

Phonolite, hills of.

-laminated.

-with more fusible hornblende.

Pitchstone.

-dikes of.

Plants, extinct.

Plutonic rocks, separation of constituent parts of, by gravity.

Porto Praya.

Prevost, M.C., on rarity of great dislocations in volcanic islands.

Prosperous hill, St.Helena.

Pumice, absent at the Galapagos archipelago.

-laminated.

Puy de Dome, trachyte of.

Quail island, St.Jago.

Quartz, crystals of, in beds alternating with obsidian.

-crystallised in sandstone.

-fusibility of.

-rock, mottled from metamorphic action with earthy matter.

Red hill.

Resin-like altered scoriae.

Rio de Janeiro, gneiss of.

Robert, M., on strata of Iceland.

Rogers, Professor, on curved lines of elevation.

Salses, compared with tuff craters.

Salt deposited by the sea.

-in volcanic strata.

-lakes of, in craters.

Sandstone of Brazil.

-of the Cape of Good Hope.

-platforms of, in New South Wales.

Schorl, radiating.

Scrope, Mr.P., on laminated trachyte.

-on obsidian.

-on separation of trachyte and basalt.

-on silex in trachyte.

-on sphaerulites.

Seale, Mr., geognosy of St.Helena.

-on dikes.

-on embedded birds' bones.

Seale, on extinct shells of St.Helena.

Sedgwick, Professor, on concretions.

Septaria, in concretions in tuff.

Serpulae on upraised rocks.

Seychelles.

Shells, colour of, affected by light.

-from Van Diemen's land.

-land, extinct, at St.Helena.

-particles of, drifted by the wind at St.Helena.

Shelly matter deposited by the waves.

Siau, M., on ripples.

Signal Post Hill.

Silica, deposited by steam.

-large proportion of, in obsidian.

-specific gravity of.

Siliceous sinter.

Smith, Dr.A., on junction of granite and clay-slate.

Spallanzani on decomposed trachyte.

Specific gravity of recent calcareous rocks and of limestone.

-of lavas.

Sphaerulites in glass and in silicified wood.

-in obsidian.

Sowerby, Mr.G.B., on fossil-shells from Van Diemen's land.

-from St.Jago.

-land-shells from St.Helena.

St.Helena.

-crater of elevation of.

St.Jago, crater of elevation of.

-effects of calcareous matter on lava.

St.Paul's rocks.

Stokes, Mr., collections of sphaerulites and of obsidians.

Stony-top, Little.

-Great.

Stratification of sandstone in New South Wales.

Streams of obsidian.

Stutchbury, Mr., on marine remains at Otaheite.

Subsided space at Ascension.

Tahiti.

Talus, stratified, within tuff craters.

Terceira.

Tertiary deposit of St.Jago.

Trachyte, absent at the Galapagos archipelago.

-at Ascension.

-at Terceira.

-decomposition of, by steam.

-its lamination.

-its separation from basalt.

-softened at Ascension.

-specific gravity of.

-with singular veins.

Trap-dikes in the plutonic series.

-at King George's sound.

Travertin at Van Diemen's land.

Tropic-bird, now rare, at St.Helena.

Tuff, craters of.

-their breached state.

-peculiar kind of.

Turner, Mr., on the separation of molten metals.

Tyerman and Bennett on marine remains at Huaheine.

Valleys, gorge-like, at St.Helena.

-in New South Wales.

-in St.Jago.

Van Diemen's land.

Veins in trachyte.

-of jasper.

Vincent, Bory St., on bombs.

Volcanic bombs.

-island in process of formation in the Atlantic.

-islands, their distribution.

Wacke, its passage into lava.

Wackes, argillaceous.

Webster, Dr., on a basin-formed island.

-on gypsum at Ascension.

White, Martin, on soundings.

Wind, effects of, on the form of craters.

End