Page 7 - Atlas of Sedimentary Rocks Under The Microscope

Preface

The study of rocks using thin sections and a petrographic microscope carbonaceous rocks in thin section. We hope the section on evaporites
was initiated by llcnry Clifton Sorby in the middle of the nineteenth will be of particular interest, as published colour photomicrographs or
century and the first rocks he described were silicified limestones from some minerals arc rare.
the Jurassic in Yorkshire. This work was published in 1851. His Three appendices arc included. Appendix I is a slightly modified
presidential address to the Geological Society of London in 1879 was form oft he a ppcndix in the !It/as a/igneous rocks and their texll/res and
entitled 'On the structure and origin of limestones' and Sorby had a describes how a thin section may be made. Appendix 2 describes a
series of plates. made from camera Iucida drawings, reproduced for method of staining thin sections of limestones and Appendix 3
private circulation with copies of the text of his address. These contains instructions on how to make acetate peels.
illustrated the microscopic characteristics oflimestones from through­ Throughout the book we have tried to keep the text descriptive and
out the British geological record and amounted to the first petro­ to avoid dctai Is of i ntcrprcta t ion. However. it has proved impossible to
graphic atlas. omit discussion in some cases, particularly with the carbonate rocks
Despite the pertinence of Sorby's work, much of which is still valid where identification of grains and textures goes hand in hand with an
today, few people recogni;ed its importance at the time. While the interpretation of their origin. We have allcmpted to show typical
petrographic study of igneous and metamorphic rocks became material rather than particularly good examples of any feature
increasingly important. that of sedimentary rocks languished until well illustrated. Extcn!-.IVC cross-referencing is given to help the reader in
into the present century. Since about 1950. with much geological finding other photographs of similar phenomena.
research directed toward� the search for oil and gas trapped in the Inevitably the bulk of the illustrated material comes from the British
pore-spaces of sedimentary rocks, sedimentary petrography has Isles: we believe howc,cr that it is representative of sedimentary rocks
become one of the most important fields of geology and forms a key the world over.
part of most undergraduate courses. Finally, we mu�t repeat the cautionary note in the preface to Atlas of
The aim of this book is therefore similar to that of the previously igneous rock.\ and their texture.\. This book is a laboratory handbook to
published Atlas <>l1'Kneo11s rocks and their texwres, in that it is designed a.uist in the �tudy of scdimentt�ry rocks in thin section. There is no
to be a laboratory handbook for the student beginning a study of substitute for the student examining material under the microscope for
sedimentary rocks in thin section, whether he or she is an amateur or him- or herself and we hope this book will encourage students to make
their own petrographic observations.
an undergraduate. Only a basic knowledge of mineralogy and palaeon­
tology is assumed. While we make no claim that the book is
comprehensive, we have tried to include photographs of most of the
components of sedimentary rocks encountered in thin sections during
an undergraduate course in geology.
The book is in three parts. Part I det�ls with the terrigenous clastic
rocks and concentrates on sandstones. since the petrographic micro­ Acknowledgements
scope is most usefully employed with rocks of this grain size. We have
a \lcmptcd to show the common del rita I components of sandstones and Although this book is based on thin sections and acetate peels held in
the range of rock types occurring. without becoming involved in the teaching collections of the Department of Geology, University of
details of the many classifications which exist. Manchester, it would not have been possible without the generous loan
Part 2 deals with the carbonate rocks and is the longest section in the of material from the research collections of many colleagues. We are
book. This is because to the newcomer to carbonate petrology, particularly indebted to Professor Sir Frederick Stewart who loaned
limestones contain a bewildering variety of grain types. The bioclasts much of the material for the evaporites section. We are grateful to Drs.
in particular show such variation in shape and structure that it has J. M. Anketell, P. Gutteridgc. J. Kantorowicz. J. E. Pollard. A. T. S.
been difficult to know what to leave out. We have attempted to show Ramsay, K. Schofield, Mr R. D. Vaughan and Professor E. K. Walton,
the range of common bioclast types while realizing that this section of all of whom loaned material and made suggestions or comments on the
the book cannot be comprehensive within the limits of the number of manuscript. We would also like to thank Professor J. B. Dawson for
photographs which we arc able to reproduce. Most of the photographs permission to include a photograph of one of Sorby's thin sections
of limestones arc from stained thin sections and acetate peels. The from the collection held at Sheffield University.
staining aids identification of minerals and textures and also makes We wish to thank Patricta Crook for her patient typing of various
limestones more attractive to study. The reader examining a collection versions of the text and Phil Stubley for drafting the originals of the
diagrams. Finally we wish to acknowledge the help given to us by all
of unstained section� of carbonate rocks should still find the photo­
graph� and text useful 111 identifying grain types and textures. the staff of the Longman Group.
Photographs of unstained limestone sections arc included throughout We acknowledge permission from Springer Verlag and Professor F.
to remind the reader what untreated material looks like. J. Pettijohn to reproduce Figs. A and D, and the American Association
Part � illustrntcs ironstone�. cherts. evaporites, phosphorites and of Petroleum Geologists for Figs. E and F and Tables 3 and 4.