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364 PHYSIOGRAPHY FOR ADVANCED STUDENTS

CHAP.

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Physical Features of Mars.—The planet Mars generally presents the aspect of a ruddy disc, which is, as before remarked,

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Fig. 162.-Mars on August 29, 1894, showing the Planet in the Gibbous phase.

(From a Drawing by Mr. Percival Lowell in The Astrophysical Journal, No. 128).

gibbous in form at stated times. Its surface markings can be distinctly made out with a telescope having a four- or five-inch

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1892, August 17d., roh. 32m.

1892, August 17d., ith. 55m. Fig. 163.-The Planet Mars, as drawn by Prof. James E. Keeler on August 17.

1892. The South Polar Cap is shown in each of the Drawings.

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.

ELEMENTARY LESSONS

IN

PHYSICAL GEOGRAPHY

BY

SIR ARCHIBALD GEIKIE, F.R.S.

(First Edition 1877 ; reprinted 1878, 1880, 1882 (2), 1883 (2), 1884. Second Edition 1884; reprinted 1886, 1887, 1889, 1890, 1892, 1894, 1897 (2), 1898 (2), 1899.)

London
MACMILLAN AND CO., LIMITED

NEW YORK: THE MACMILLAN COMPANY

Academy—“The language is always simple and clear, and the descriptions of the various phenomena are no less vivid than interesting; the lessons are never dull, never wearisome, and they can scarcely fail to make the study of Physical Geography popular wherever they are used,"

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xxvi.]

LAKES AND INLAND SEAS.

279

5. (2) A further feature in the distribution of lakes, which may be observed on maps, is the more or less abundant occurrence of these sheets of water among

Fig. 53.--Section of a lake-basin lying in a hollow of superficial detritus. mountains. Take Europe as an illustration. Even in the comparatively low mountain groups of Scotland, Cumberland, and Wales, lakes abound, forming one of the great charms of the well-known scenery of these districts. Among the Alps a series of large lakes occurs on each side of the main axis of the chain, and innumerable minor sheets of water occur scattered at all heights among the central mountains, up even to the borders of the snow-line. All mountain systems, indeed, have not

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Fig. 54.-Section of a lake dammed up by a barrier of earth or gravel. the same abundance of water-filled hollows; in some there are few or none. Lakes among mountains may be, in some cases, hollows formed during the elevation of the mountains (Lesson XXIX.); in other examples, like those referred to in Art. 4, they may either have had their basins scooped out by glaciers or formed by the irregular piling up of ice-borne debris (Fig. 54). In most volcanic districts, lakes occur in cavities which

ve been formerly blown open by explosions from

1892,

Fig. 163.-The Planet Mars

1892. The South Polar

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Geology for Beginners

BY

W. W. WATTS, M.A., F.G.S.

FORMERLY LECTURER TO THE CAMBRIDGE UNIVERSITY EXTENSION
AND MEMBER OF HER MAJESTY'S GEOLOGICAL SURVEY, AND
NOW ASSISTANT-PROFESSOR IN GEOLOGY AT THE

BIRMINGHAM UNIVERSITY

WITH THREE HUNDRED AND TEN ILLUSTRATIONS

London
MACMILLAN AND CO.,

LIMITED

NEW YORK: THE MACMILLAN COMPANY

All rights reserved

Ar the present time there appears to be needed a small book on Geology which, while short and elementary in treatment, is accurate and fairly up to date. Further, it is well that sections and diagrams should be supplemented by photographs of hand-specimens and microscopic slides of rocks, and of the natural exposures where rocks are to be seen in the field. The author has kept both these aims in view while planning his work on the lines of the revised syllabus of the Science and Art Department.

While primarily intended for use in preparation for the elenientary stage of the Science and Art Examination, care has been taken to make the book suitable for school work and for the examinations of the Oxford and Cambridge Schools' Examination Board. With this object in view there have been placed at the end of the chapters all the Questions set in the Science and Art Examination during the last twenty years, and those of the Oxford and Cambridge Board for ten years.

Naturally in writing this book no other elementary work of the class has been consulted, but no one who has ever read the late Professor Green's classic work on Physical Geology can help being attracted by the lucidity of his style and influenced by the charm of his methods. The writer owes an especial debt for the advice and assistance given him when acting as Professor Green's deputy on two occasions several years ago. The principal methods pursued in two or three of the earlier chapters, and the general practical aim of the book as a whole, are due directly to Professor Green's advice.

CONTENTS

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CHAPTER I. Introduction ; II. Study of a Piece of Stone at Home ; III. Study of Rocks out of Doors; IV. Wear and Tear of Rocks by the Weather and Springs; V. Denudation by Rivers and Glaciers; VI. Marine Denudation-Rate of Work; VII. Rock-building by Sediments ; VIII. Rock-structures and Earth-movement; IX. Faulting, Cleavage, and Joints ; X. Minerals; XI. Sedimentary Rocks; XII. Volcanoes; XIII. Volcanic Rocks; XIV. Plutonic Rocks; XV. Foliated Rocks; XVI. Fossils ; XVII. Principles of Historical Geology ; XVIII. The Eozoic and Older Palæozoic Groups ; XIX. The Palæozoic Group -Deutozoic Division ; XX. The Neozoic Group-Mesozoic Division; XXI. The Neozoic Group-Cainozoic Division ; XXII. The Origin of Landscape ; XXIII. Economic Geology.

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