Part 2

PLATE IX. LIFE NEAR THE SNOW LINE; THE BOG-COTTON IN POSSESSION. NEAR THE TSCHINGEL PASS, SWITZERLAND - to face p. 80

PLATE X. 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

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.

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 much attention within recent years. The age of the Earth is, indeed, of primary importance in our conception of the longevity of planetary systems. The essay deals with the evidence, derived from the investigation of purely terrestrial phenomena, as to the period which has elapsed since the ocean condensed upon the Earth's surface. Dr. Decker's recent addition to the subject appeared too late for inclusion in it. He finds that the movements (termed isostatic) which geologists recognise as taking place deep in the Earth's crust, indicate an age of the same order of magnitude

as that which is inferred from the statistics of denudative history.

The subject of Denudation naturally arises from the first essay. In thinking over the method of finding the age of the ocean by the accumulation of sodium therein, I perceived so long ago as 1899, when my first paper was published, that this method afforded a means of ascertaining the grand total of denudative work effected on the Earth's surface since the beginning of geological time; the resulting knowledge in no way involving any assumption as to the duration of the period comprising the denudative actions. This idea has been elaborated in various publications since then, both by myself and by others. "Denudation," while including a survey of the subject generally, is mainly a popular account of this method and its results. It closes with a reference to the fascinating problems presented by the inner nature of sedimentation: a branch of science to which I endeavoured to contribute some years ago.

Mountain Genesis first brings in the subject of the geological intervention of radioactivity. There can, I believe, be no doubt as to the influence of transforming elements upon the developments of the surface features of the Earth; and, if I am right, this source of thermal energy is mainly responsible for that local accumulation of wrinkling which we term mountain chains. The

Bull. Geol. Soc. America, vol. xxvi, March 1915.