Rocks and Their Origins

Name: Rocks and Their Origins
Author: Cole, Grenville A. J. (Grenville Arthur James)

Cole, Grenville A. J. (Grenville Arthur James)

Rocks

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._




CONTENTS


  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

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Rocks and Their Origins

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