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CHAPTER XXVIII.
ISLANDS LYING TO THE WEST OF AFRICA.
Canaries.-Teneriffe, its basaltic rocks, trachytes, lavas.-Palma, its
Caldera.-Great Canary-Fortaventura-Lancerote - Madeira-
Porto Santo.-Azores-St. Michael-Terceira-Flores-Graciosa-
Atlantis of the ancients.-Cape Verde Islands-Fuego-St. Jago.—
Islands south of the Equator-Ascension-St. Helena-Fernando
Noronha-Tristan d'Acunha .................
CHAPTER XXIX.
WEST INDIAN ARCHIPELAGO.
Page
.... 442
Division of the Islands into four classes:-1st class-Trinidad, its
pitch-lake-Jamaica, extinct volcano-Cuba, upraised beach-St.
Domingo-Porto Rico.-2nd class-Grenada-St. Vincent-St.
Lucia-Martinique― Dominica-Guadeloupe-Montserrat-Nevis
-St. Christopher's-St. Eustachia.-3rd class.-4th class-Antigua 465
CHAPTER XXX.
VOLCANOS OF NORTH AMERICA, OR ABOVE THE ISTHMUS
OF DARIEN.
North and Central America-Oregon Territory-California-Mexico
-Guatemala
474
CHAPTER XXXI.
VOLCANOS OF SOUTH AMERICA, OR SOUTH OF THE ISTHMUS
General character of the Volcanos of South America-those of Quito
-of Peru-Bolivian Andes plutonic-Cordilleras of the coast vol-
canic-Chili-Patagonia-Tierra del Fuego-South Shetland-
General remarks
485
PART II.
ON PHENOMENA NOT IMMEDIATELY ARISING FROM VOL- CANOS, BUT SUPPOSED TO BE CONNECTED WITH THEM.
CHAPTER XXXII.
ON EARTHQUAKES.
1st. THE NATURE OF THE EARTHQUAKE-SHOCK.—Earthquakes defined. Three kinds of shock: undulating- succussive-and vor-
ticose-examples of the three kinds.-Instruments for registering
earthquake-shocks.--Central earthquakes-linear ones.- Duration
of shocks-noises which accompany them-recurrence of shocks—
diffusion of shocks through different strata-shocks felt at sea.-
2nd. DYNAMICS OF EARTHQUAKES-Mr. Mallet's views stated... 507
CHAPTER XXXIII.
THE CONCOMITANTS, EFFECTS, CAUSES, AND THE PHYSICAL
CHANGES BROUGHT ABOUT BY THEM.-Flames and gases emitted
during earthquakes.-Their influence upon the barometer. Physical
changes resulting from them-fissures in the earth-elevations and
depressions of the land occasioned. Connexion between earthquakes
and volcanos-shown in the case of that of Lisbon-the Caraccas-
the West Indies-Scotland. Earthquakes do not arise from elec-
tricity—or from the falling-in of caverns. Their probable influence ·
upon the structure of the globe-in elevating and submerging tracts
of land, &c. ...... 527
CHAPTER XXXIV.
THERMAL SPRINGS-THEIR GEOLOGICAL POSITION.
SALSES OR MUD-VOLCANOS-improperly designated by the latter
name--not being amongst the primary effects referable to the action
of volcanic forces.
THERMAL SPRINGS-afford indications of languid volcanic action.—
This proved by their immediate connexion with volcanos-active—
or extinct-or where not so circumstanced, by being placed at the
foot, or in the midst, of some chain of mountains that has been ele-
vated.—Instances of the latter in the Pyrenees-in the Alps.—
Where not connected with any great system of mountains, they often
proceed from rocks which show evidences of dislocation.-Examples
of this, in the thermal springs of Bristol-of Matlock-of Carlsbad-
of St. Paul near Carcassone-of Pfeffers-in those of Virginia, &c. 539
CHAPTER XXXV.
THERMAL WATERS, THEIR GASEOUS IMPREGNATION, ETC.
Gases evolved from thermal waters.-Nitrogen-at Bath, its quantity
-Buxton, &c.— Cardiff — Clifton - Pyrenees-Alps — Ceylon—
United States. Sulphuretted hydrogen.-Carbonic acid.-Petrify-
ing springs.-Valleys of elevation emitting carbonic acid.-Perma-
nency of physical and chemical properties belonging to thermal
waters. Conclusions deduced from these premises as to the con-
nexion between thermal waters and volcanos.-Tabular view of the
properties and temperature of the best-known thermal waters
557
PART III.
DEDUCTIONS FROM THE FOREGOING FACTS: WITH REFER-
ENCE TO THE CAUSES OF VOLCANOS; THE CIRCUM-
STANCES THAT INFLUENCE THE CHARACTER OF THEIR
PRODUCTS; AND THE USES THEY FULFIL IN THE ECO-
NOMY OF NATURE.
CHAPTER XXXVI.
GENERAL STATEMENT OF THE VARIOUS THEORIES BY
MEANS OF WHICH THE OPERATIONS OF VOLCANOS
HAVE BEEN ACCOUNTED FOR.
Two classes of theories, chemical and mechanical. Chemical-Le-
mery's, Breislac's, Davy's-the latter view shown not to be antece-
dently improbable. The Mechanical theory founded on the internal
heat of the globe briefly sketched.-Necessity, in order to decide
to which the preference is due, of ascertaining in what degree either
one is competent to afford an explanation of the phænomena
CHAPTER XXXVII.
.... 593
GENERAL INFERENCES RESPECTING THE LAWS OR
CONDITIONS OF VOLCANIC ACTION.
Local distribution of volcanos-in lines—and in groups-their general
proximity to the sea.-Aëriform fluids evolved.—Bodies not perma-
nently elastic which are evolved as vapours.—Bodies in a solid state
ejected—viz. 1st, lavas, their chemical characters-2ndly, loose frag-
ments thrown out. Relation of these bodies to trachyte-trachyte
whence derived.
Depth at which volcanic operations proceed. Constitution of a vol-
canic mountain-mode of its formation. Production of a crater-
by eruption-by elevation.-Proofs of the elevation of volcanic
mountains-1st, from their own internal structure-2ndly, from the
existence of domes of trachyte-3rdly, from the continuous sheets
of volcanic matter overspreading large districts-4thly, from the
testimony of eye-witnesses in the case of Santorino-Unalaschka-
Graham's Island-Monte Nuovo-Jorullo, &c.
Statement of Von Buch's views with regard to craters of eruption and
of elevation
CHAPTER XXXVIII.
COMPARATIVE ESTIMATE OF THE MECHANICAL AND
CHEMICAL THEORIES.
The two theories equally based upon assumptions.-Mechanical theory
explains the protrusion of lava-but does not explain the position of
603
volcanos or other circumstances connected with them-such as the
steam and gases evolved—the upheaving force, &c.— Theory modi-
fied by supposing water to take part in the operations--gases evolved
not explained by this addition-hence combustion of some kind must
be inferred-that of the metals of the earths and alkalies affords the
most ready solution of the phænomena. Objections answered. This
view explains the long continuance of the action exerted-mean
density of the earth shown to be no objection to it
637
...........
......
CHAPTER XXXIX.
STATEMENT OF THE CHEMICAL THEORY OF VOLCANOS.
Primordial condition of the globe nebular-sinking of temperature
down to the point at which the denser bodies became liquid-further
sinking to the point at which chemical action commenced-water
and muriatic acid first formed-action of these bodies upon the metals
forming the crust of the globe-contraction of the crust from cooling
-admission of water to the interior of the earth a natural consequence
of this contraction-formation of volcanic products arising out of this
-muriatic acid-sulphuretted hydrogen and other gases evolved-
the whole of the hydrogen not emitted from the crater.–Formation
of ammonia--of carbonic acid-disengagement of nitrogen explained.
-Heat diffused through the crust in consequence of the chemical
actions set up
Concluding remarks.—Degree of probability attributed to the different
points which the Chemical Theory embraces.-Reasons for putting
it forward more prominently than its intrinsic probability may seem
to justify
646
CHAPTER XL.
ON THE ROCKS ATTRIBUTED TO VOLCANIC AGENCY TAKING
PLACE UNDER CIRCUMSTANCES DIFFERENT FROM THOSE
BEFORE CONSIDERED.
Trap rocks—their general characters, their structure--prismatic-
spheroidal-tabular-Dykes-Wernerian theory with regard to trap.
-Arguments in favour of the aqueous origin of basalt-shown to be
fallacious.—Difference between lavas and basalts explained.—Effects
of heat modified by pressure.—Why submarine lavas cool slowly-
causes that give rise to vitreous products—lamination of igneous
products accounted for.— Process of devitrification referred to slow
cooling-still slower cooling may produce basalt and other traps.
- Why submarine lavas have cooled slowly.-- Prismatic structure
of trap accounted for.-Greater frequency of dykes.— Trap rocks,
at what periods formed.— Three classes of volcanic products-their
characters stated.—Distinctions between plutonic and volcanic
rocks
658 CHAPTER XLI.
FINAL CAUSES OF VOLCANOS.
Volcanos act as safety-valves by which earthquakes are prevented-
as agents in elevating chains of mountains-are instrumental in sup-
plying plants with carbonic acid-and with ammonia.- Formation
of ammonia in the interior of the earth.-Volcanos also furnish the
inorganic constituents necessary for the food of plants—and in a
condition in which they can be slowly taken up-render phosphate
of lime soluble in water--and evolve it from the depths of the earth
--return back to the surface the water which finds its way into the
bowels of the earth-contribute to the production of mineral veins.
— Their influence in communicating fertility shown in the case of
the Campagna about Naples.-Desolation caused by an eruption
not permanent............
691
APPENDIX,
CONTAINING ADDITIONAL NOTES, AND LIST OF WORKS ON
VOLCANOS, EARTHQUAKES, AND THERMAL WATERS.
On the Rhöngebirge
707
On the Theory of Dolomisation
On the Temple of Serapis at Puzzuoli
709
On the Height of the Cone of Vesuvius
710
Professor Bunsen on Iceland ...........
On the Period of the Formation of the Dead Sea
714
On Volcanic Appearances in the neighbourhood of the Red Sea 714
On the Typhon or Typhæus of the Greeks
716
On the Nicobar Islands
720
On the Geological Structure of Kerguelen's Land
Cacciatore's Seismometer
721
On Paroxysmal Actions
On the Origin of the Carbonic Acid discharged from Volcanos 722
Reply to Professor Bischof's Further Reasons against the Chemical
Theory of Volcanos
722
On the Tertiary Lavas
725
On the Oscillations of Opinion with respect to the Origin of Trap 727
On the Existence of Iodine and Bromine in the earliest Seas
728
List of Works on Volcanos
729
List of Works on Earthquakes .....
742
List of Works on Thermal Springs
........