Rocks and Their Origins - Grenville A. J. Cole

With the exception of the coat of arms at
the foot, the design on the title page is a
reproduction of one used by the earliest known
Cambridge printer, John Siberch, 1521

PREFACE

This little book is intended for those who are not specialists in geology, and it may perhaps be accepted as a contribution for the general reader. To all who are interested in the earth, the study of rocks is an important branch of natural history. If detailed works on petrology are to be consulted later, F. W. Clarke's Data of Geochemistry (Bulletin, U.S. Geological Survey, ed. 2, 1911) must on no account be overlooked. Its numerous references to published papers, and the attention given to rock-origins, make it a worthy companion to C. Doelter's Petrogenesis. Many things have perforce been omitted from the present essay. It seemed unnecessary to review the Carbonaceous rocks, since the most important of these have been admirably dealt with in E. A. N. Arber's Natural History of Coal, published as a volume in this series. I should like to have described occurrences of rock-salt, of massive gypsum, and other products of arid lands, where "black alkali" poisons the surface, and the casual pools are fringed with white and crumbling crusts. Rock-taluses, and all the varied alluvium carried seaward as the outwash of continental land, well deserve a chapter to themselves. But there is really no end to the subject, which embraces all the accumulative processes of the earth. A few vacation-journeys, judiciously planned out, teach us that text-books are merely signposts to set us on what is believed to be the way. When the path enters the great forest, or rises above green lakelets to the crags, we find there those who went before us, pointing to unconquered lands.

G. A. J. C.

Royal College of Science
for Ireland, Dublin.
February 1912.

CHAP.		PAGE
	List of Illustrations	[viii]
I.	On Rocks in General	[1]
	List of the common Minerals that form Rocks	[8]
II.	The Limestones	[12]
III.	The Sandstones	[56]
IV.	Clays, Shales, and Slates	[78]
V.	Igneous Rocks	[103]
VI.	Metamorphic Rocks	[143]
	References	[162]
	Table of Stratigraphical Systems	[189]
	Index	[170]

LIST OF ILLUSTRATIONS

Fig.		PAGE
1	Surface of Limestone plateau, Causse du Larzac, Aveyron	[45]
2	Ravine in Limestone, Cañon of the Dourbie, Aveyron	[47]
3	Waterworn cliff of Limestone, Millersdale	[49]
4	Limestone country dissected by ravines, Hercegovina	[51]
5	Sand developing from Sandstone, Cape of Good Hope	[59]
6	Siliceous Conglomerate, Co. Waterford	[75]
7	Quartzite Cone, Croagh Patrick	[77]
8	Shrinkage-cracks in Clay, Spitsbergen	[81]
9	Landslide of Limestone over Shale, Drôme	[93]
10	Weathering of Shale, Isère	[95]
11	Boulder-clay, Crich, Derbyshire (Phot. H. A. Bemrose)	[97]
12	Nordenskiöld Glacier, Spitsbergen	[99]
13	Sefström Glacier, Spitsbergen	[101]
14	Ash-layer of 1906 on Vesuvius	[111]
15	Puy de la Vache, Puy-de-Dôme	[113]
16	Granite invading Mica-schist, Cape Town	[121]
17	Weathering granite, Lundy Island	[139]
18	Granite weathering under tropical conditions, Matopo Hills	[141]
19	Composite Gneiss, Co. Donegal	[153]
20	Composite Gneiss, Ängnö, Sweden	[155]

(Figs. [11] and [17] are reproduced from the Cambridge County Geographies of Derbyshire and Devonshire respectively; the rest of the illustrations are from photographs by the author.)

PREFACE

CONTENTS

LIST OF ILLUSTRATIONS