Physical Geography. Fourth edition ... revised. With a portrait

Front matter

ca /'/;/ wm ? ''/œ Xoaacam. John Kaiir*/, Albeaaaarifa S^ . ■ SB PHYSICAL GEOGRAPHY. By MARY. SOMERVILLE, AUTHOR OF THE ' CONNEXION OF THE PHYSICAL SCIENCES, 'MECHANISM OF THE HEAVENS,' ETC. ETC. FOURTH EBITION, THOROUGHLY REVISES. WITH A PORTRAIT. LONDON: JOHN MUEEAY, ALBEMAELE STEEET. 1858. BY THE SAME AUTHOR. ON THE CONNEXION OF THE PHYSICAL SCIENCES. Ninth and Revised Edition, Portrait and Woodcuts, Post Svo. " The style of this astonishing production is so clear and unaffected, and conveys with so much simplicity so great a mass of profound knowledge, that it should be placed in the hands of every youth the moment he has mastered the general rudiments of education." — Quarterly Review. LONDON : PRINTED BT W. CLOWES AND SONS, STAMFORD STREET, AND CHARING CROSS. TO SIE JOHN F. W. HERSCHEL, Bart., K.H., 4-c. $c, $c. Dear Sir John, I have much pleasure in again availing myself of your per mission to inscribe this book to you, as it gives me an opportunity of assuring you once more of my admiration of your talents, my high appreciation of the services you have conferred upon science, and of my sincere estimation of your friendship. I remain, with great regard, Yours truly, Mart Somerville. Florence, November, 1857. a

Preface

TO THE FOURTH EDITION. The recent rapid progress of science and the numerous expeditions by sea and land, not for mere amusement, but for high scientific research, have caused the accumulation of such a mass of valuable geographical information, that it is difficult to select the leading features where the inte rest is so extensive, and still more so to condense them within the narrow limits of a work like the present. In many instances newly discovered facts have so modified received opinions, that it has been necessary to add much new matter, and remodel several of the chapters in this volume. In the former editions the Author acknowledged her obligations to Baron Humboldt's invaluable Cosmos, with General Sabine's excellent notes ; to the works of Sir Charles Lyell, which have so much contributed to popu larise Geology wherever the English language is read or spoken ; ' to the researches of Messrs. Strachey, Thomson, and Dr. Joseph Hooker2 on the Himalaya, and to the papers in the numerous periodical publications of Europe, India, and the United States.

In the present she must express her gratitude to others whose discoveries and researches have so largely contributed to the improvement of this, and in particular to Sir Eoderick Murchison, who amongst our countrymen stands unrivalled in everything connected with Geology— to Professor H. D. Eogers of Glasgow, formerly of the United States, for his account of the Physical Geography and Geology of the North American Continent. The surveys that have been exe- ' Principles of Geology,' by Sir Charles Lyell, 8vo. ; ' Manual of Ele mentary Geology,' by Sir Charles Lyell, 8™. ; 'The Geological Observer,' by Sir Henry T. De la Beche, C.B., 8vo., 1851. Hooker's ' Himalayan Journals,' Thomson's ' Western Tibet.' a

PREFACE.

TO THE FOURTH EDITION. VI cuted with a view of establishing canals and railways across Central America have furnished much new information with regard to a country which has become of more interest since the discovery of great auriferous riches in California. The travels of Colonel and Mr. Strachey, the labours of several British officers in Tibet and the Himalaya, and the continuation of the Survey of British India under the able direction of Colonel Waugh, have opened new views with regard to the most elevated regions of the Asiatic Continents ; whilst the Discoveries of Dr. Livingstone in South Africa, made in subordination to much higher objects, and those of Dr. Barth and his com panions in the Northern part of that Continent, have enabled the Author to give a more accurate view of countries that have been until now a terra incognita.

This was also the case as regards Northern Australia before the late able survey of Mr. Gregory. The following pages will show how highly the Physical Geography of the Ocean, by Lieutenant Maury, has been appreciated by the Author ; and the extent of information she has collected from the surveys and narratives of the brave and able officers, both of her own country and of the United States, in their perilous examinations of the Arctic Eegions in search of the everto-be-lamented Franklin. On the subject of the Tides Dr. Whewell's labours have been her great authority and guide, as those of her friends General Sabine and Mr. Faraday on Terrestrial Magnetism. In this, as well as in former editions, the Author has availed herself largely of the invaluable labours of Mr. Alexander Keith Johnston.1 The new edition of his Atlas of Physical Geography in folio, published during the past year, has been of the greatest service to her in the com pilation of the present volume,2 as also the Geographical 1 ' The Physical Atlas of Natural Phenomena,' 1 vol. fol. 2nd edit. 1856 ; ' The Physical Atlas, reduced for the Use of Colleges, Families, &c.,' 1 vol. 4to.; and ' The School Atlas of Physical Geography,' 1 vol. 4to. 2 It had been the author's wish, and her publisher's intention, to accompany this work with maps illustrative of the most important questions of Physical Geography, but this has been rendered unnecessary by the edition of the ' Physical Atlas ' on a reduced scale, which has been given to the public.

PREFACE.

TO THE FOURTH EDITION. VII Dictionary by the same author, the most complete and accurate work of the kind that has appeared in our own or any other language. To Sir Eoderick Murchison, Mr. George Gray, Mr. Sclater, Mr. Adam White, ofthe British Museum, who have looked over the chapters on Geology and Zoology, to Dr. Hooker and Professor Henslow, who have carefully revised those on Botany, and to Mr. Alexander Keith Johnston for his general revision of the geographical portion, the Author's best thanks are due. To her friend Mr. Pentland she must express her acknow ledgments for his kindness, during her residence abroad, in again superintending the passage through the press of this new edition, for matter hitherto unpublished on the countries visited by him in South America, and for valuable information that could only be procured in England. Florence, November, 1857. CONTENTS.

Chapter I

Geology : Of Physical Geography — Position of the Earth in the Solar System — Distance from the Sun — Civil Year — Mass of the Sun — Distance of the Moon — Figure and Density of the Earth from the Motions of the Moon — ■ Figure of the Earth from the Measure of Arcs ofthe Meridian — from Oscillations of Pendulum — Local Disturbances — Mean Density of the Earth — -Known Depth below its Surface — Outline of Geology .. .. .. .. .. .. .. Page 1

Chapter II

Direction ofthe Forces that raised the Continents — Proportion of Land and Water — Size of the Continents and Islands — Outline of the Land — Extent of Coasts, and proportion they bear to the Areas of the Continents — Elevation of the Continents — Forms of Mountains — Direction of the Chains of Mountains — Connexion between Physical Geography of Countries and their Geological Structure — Contemporaneous Upheaval of parallel Mountain Chains — Mr. Hopkins's Theory of Fissures — Parallel Chains similar in Structure — Interruptions in Continents and Mountain Chains — Form of the Great Continent — The High Lands ofthe Great Continent — The Atlas, Spanish, French, and German Mountains — The Alps, Balkan, and Apennines — Glaciers — Geological Notice .. .. ..27

North America, continued— The Great Central Plains, or Valley ofthe Mississippi — The Alleghany Mountains — The Atlantic Slope — The Atlantic Plain — Geological Notice — The Mean Height of the Continents .. 129

Chapter XIII

The Continent of Australia — • Tasmania, or Van Diemen's Land — Islands — Continental Islands — Pelasgic Islands — -New Zealand — New Guinea — ■ Borneo — Atolls — Encircling Reefs — Coral Reefs — Barrier Reefs — Volcanic Islands — -Areas of Subsidence and Elevation in the Bed of the Pacific — Active Volcanoes — Earthquakes — Secular Changes in the Level ofthe Land .. .. 141

Chapter XIV

Arctic Lands — Greenland — Spitzbergen — Iceland — Its Volcanic Phenomena and Geysers — Jan Mayen Land — ■ New Siberian Islands ■ — - Antarctic Lands — Victoria Continent .. .. .. .. ..167

Chapter XV

Nature and Character of Mineral Veins — Metalliferous Deposits — Mines — Their Drainage and Ventilation — Their Depth — Diffusion of the Metals — Gold — Silver — Lead — British Mines — Quicksilver — Copper — Tin — Cornish Mines — Coal — Iron — Most abundant in the Temperate Zones, especially in the Northern — European and British Iron and Coal — American Iron and Coal — Arsenic and other Metals — Salt — Sulphur — Diffusion of the Gems .. .. .. .. .. .. 177

Chapter XVI

The Ocean — its Size, Colour, Pressure, and Saltness — Tides — Waves — their Height and Force — Currents — their Effect on Voyages — Temperature — The Stratum of Constant Temperature — Line of Maximum Temperature — North and South Polar Ice — Inland Seas . . . . CONTENTS. XI

River Systems of North America — Rivers of Central America — Rivers of South America and of Australia .. .. .. .. .. 258

Chapter XX

Lakes in general — European Lakes — Northern Europe — Of the Pyrenees, Alps, and Italy — Lake of Tiberias and Dead Sea — Asiatic Lakes ■ — Caspian — Lakes of Aral, Baikal, and ofthe Himalaya — Sacred Lakes of Manasarowar — African Lakes — Bahr Assal — ■ Zambeze — Ngami — American Lakes in Canada — Nicaragua — Titicaca .. .. .. 270

Chapter XXI

Temperature of the Earth — Temperature of the Air — Radiation — Foci of Maximum Cold — Thermal Equator — Its Temperature, mean and absolute — Isothermal Lines — Continental and Insular Climates — Extreme Climates — Stability of Climate — Decrease of Heat in Altitude — Line of Perpetual Snow — Density of the Atmosphere — The Barometer — Measurement of Heights — Variations in Density and their Causes — Horary Variations — Independent Effect of the dry and aqueous Atmospheres — Mean Height of Barometer in different Latitudes — Depression in the Antarctic Ocean and in Eastern Siberia — Barometric Storms — Polar and Equatorial Currents of Air — Trade Winds — Monsoons — Land and Sea Breezes — Gyration of the Winds in the Extra-Tropical Zones — Winds in Middle European Latitudes — Hurricanes — The Laws of their Motion — Their Effect on the Barometer — How to steer clear of them — The Storm- Wave — Storm-Currents — Arched Squalls — Tornadoes — Whirlwinds — Water-Spouts 279

Chapter XXII

Evaporation — Distribution of Vapour — Dew — Hoar-Frost — Fog — Region of Clouds — Forms of Clouds — Rain — Distribution of Rain — Quantity — Number of rainy Days in different Latitudes — Rainless Districts — Snow Crystals — Line of Perpetual Snow — Limit of Winter Snow on the Plains — Sleet — Hail — Minuteness of the Ultimate Particles of Matter — Their Densities and Forms — Their Action on Light — Colour of Bodies — Colour of the Atmosphere — Its Absorption and Reflection of Light — Mirage — Fog Images — Coronæ and Halos — The Rainbow — Iris in Dewdrops — The Polarization of the Atmosphere — Atmospheric Electricity — Its Variations — Electricity of Fogs and Rain — Inductive Action of the Earth — Lightning — Thunder — Distribution of Thunder-Storms — Back Stroke — St. Elmo's Fire — Phosphorescence — Aurora — Magnetism — Terrestrial Magnetism — The Dip — Magnetic Poles and Equator — Magnetic Intensity — Dynamic Equator — Declination — Magnetic Meridian — Lines of Equal Variation — Horary Variations — Line of Alternate Horary Phenomena — Magnetic Storms — Coincidence of the Lines of equal Magnetic Intensity with Mountain Chains — Diamagnetism .. .. CONTENTS.

Distribution of Mammalia .. .. .. .. _ 4.5Q