. THE JOY OF LIFE. THE AMPEZZO THAL; DOLOMITES - to face
p. 93

PLATE XI. "PINES SOLEMNLY QUIET." DUeSSISTOCK; MADERANER THAL - to
face p. 100

PLATE XII. ALPINE FLOWERS IN THE VALLEYS - to face p. 105

PLATE XIII. ALPINE FLOWERS ON THE HEIGHTS - to face p. 106

PLATE XIV. MOUNTAIN SOLITUDES; VAL DE ZINAL. FROM LEFT TO RIGHT
ROTHHORN; BESSO; OBERGABELHORN; MATTERHORN; PIC DE ZINAL (THROUGH
CLOUD); DENT BLANCHE - to face p. 116

ix

PLATE XV. SECTOR OF THE EARTH RISE OF ISOGEOTHERMS INTO A DEPOSIT
EVOLVING RADIOACTIVE HEAT - to face p. 118

PLATE XVI. "THE MOUNTAINS COME AND GO." THE DENT BLANCHE SEEN
FROM THE SASSENEIRE - to face p. 133

PLATE XVII. DIAGRAMMATIC SECTIONS OF THE HIMALAYA - to face p.
140

PLATE XVIII. RESIDUES OF DENUDATION. THE MATTERHORN SEEN FROM THE
SUMMIT OF THE ZINAL ROTHHORN - to face p. 148

PLATE XIX. THE FOLDED ROCKS OF THE MATTERHORN, SEEN FROM NEAR
HOeHBALM. SKETCH MADE IN 1906 - to face p. 156

PLATE XX. SCHIAPARELLI'S MAP OF MARS OF 1882, AND ADDITIONS (IN
RED) OF 1892 - to face p. 166

PLATE XXI. GLOBE OF MARS SHOWING PATH OF IN-FALLING SATELLITE -
to face p. 188

PLATE XXII. CANALS MAPPED BY LOWELL COMPARED WITH CANALS FORMED
BY IN-FALLING SATELLITES - to face p. 192

PLATE XXIII. HALOES IN MICA; CO. CARLOW. HALO IN BIOTITE
CONTAINED IN GRANITE - to face p. 224

PLATE XXIV. RADIUM HALO, MUCH ENLARGED. THORIUM HALO AND RADIUM
HALO IN MICA - to face p. 228

PLATE XXV. HALO ROUND CAPILLARY IN GLASS TUBE. HALOES ROUND
TUBULAR PASSAGES IN MICA - to face p. 230

PLATE XXVI. ALETSCH GLACIER, SWITZERLAND - to face p. 282

PLATE XXVII. THE MIDDLE ALETSCH GLACIER JOINING THE GREAT ALETSCH
GLACIER. GLACIERS OF THE LAUTERBRUNNEN THAL - to face p. 285

PLATE XXVIII. PERCHED BLOCK ON THE ALETSCH GLACIER. GRANITE
ERRATIC NEAR ROUNDWOOD, CO. WICKLOW; NOW BROKEN UP AND REMOVED -
to face p. 286

And Fifteen Illustrations in the Text.

x

PREFACE

Tins volume contains twelve essays written at various times
during recent years. Many of them are studies contributed to
Scientific Reviews or delivered as popular lectures. Some are
expositions of views the scientific basis of which may be
regarded as established. Others--the greater number--may be
described as attempting the solution of problems which cannot be
approached by direct observation.

The essay on The Birth-time of the World is based on a lecture
delivered before the Royal Dublin Society. The subject has
attracted