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Stereographic projection techniques in structural geology
Joamol
of Africm
Em-rh Sc;encrr.
Vol. 22, No. 4. p 625. I996 Ekvier
Pergamon
Science
Ltd
Primed m Great Bnmin
BOOK REVIEW Stereographic
projection
techniques
I’. R. LEYSHON Published
by Butterworth
Heinemann,
in structural
geology
and R. J. LISLE l996,104p.,
fZ16.99 (ISBN o-7506-2450-7)
IBM compatible disk with two programs, one of which gives the user more practice at visualising stereograms and the other being a versatile stereogram-plotting program. This latter program is not as user-friendly as some that are available (not to be attempted without manual in hand!), but it does cover all the common procedures and can be copied and distributed as required. In general, this book is a practical and workmanlike introduction to stereograms in structural geology and will be of great use to hard-pressed lecturers with large classes and limited time, particularly those nonspecialists who find themselves teaching structural geology. It is a must for all teaching libraries, preferably in multiple copies, though students would probably prefer to buy a more general structural text, if this book were available for reference. What of those outside academia - would I recommend this book to you? Certainly - if as professional geologists you feel the need for a refresher course, if stereographic analysis of your data would be useful, but you haven’t tried it since undergraduate days, or if you find yourself plotting up data and then saying ‘So what?‘. On the negative side, like any book designed to take the place of a practical demonstration, it has a tendency to wordiness; there is no real replacement for someone at the front of the lab showing the class how things are done. Simple procedures which require only a few seconds demonstration may take a couple of complex paragraphs to be successfully described on the page. Some of the field photos could have been clearer or better labelled, though this will only be a serious problem for anyone without the opportunity to see the structural features in the field. And one final small niggle - the method recommended and employed in the book is to rotate the underlying stereographic net while keeping the tracing overlay stationary. All very well for the lab, but I would maintain that on a wet and windy Scottish hilside, it is far easier having the net in my field notebook and rotating the tracing overlay!
This large-format paperback book is designed primarily as a lab manual for undergraduates following a course in structural geology. It provides an introduction to the theory of stereographic projection, as well as exhaustive instruction on how to treat the variety of structural data likely to be encountered in the course of field mapping. Each topic or method is given a page of with the facing page being precise description, illustrations(3D sketches, maps or photos as appropriate), with the accompanying fully annotated stereogram. The book begins with a section on the measurement and recording of geological structures, followed by an introduction to the concept of lower hemisphere spherical projections. The next section encourages the reader to ‘guesstimate’ their own stereograms by visualising the projection of structural elements onto the lower hemisphere. This is an interesting way of illustrating how a stereogram works, but it is doubtful whether it will help the student who has real problems with 3D visualisation in general. There is comprehensive coverage of how to plot lines and planes accurately, which evolves from simple examples like the plunge of a fold axis, to more complex exercises such as projecting apparent lineations onto a plane; most of these sections are accompanied by geological examples of situations where such methods might be employed. There is a particularly useful section on fold analysis, including fold orientation and classification, which illustrates how stereograms vary with differences in fold shape, symmetry, interlimb angle etc. A section on folds and cleavage follows; an illustration of a typical cleavage fan would have made the discussion of bedding/cleavage asymmetry somewhat clearer. A later section tackles superposed folding and the concept of subareas or structural domains. The importance of cones and small circles is described, with examples including restoration of the tilt of beds, palaeocurrent analysis and borehole problems, and there is also brief treatment of different types of net, density counting, slip on faults, jointing and geotechnical problems. Exercises set within the text are supplemented by a final exercise list (with solutions) and there is also an
Department of Geology Aberdeen University
625
S. Goodman
of Africm
Em-rh Sc;encrr.
Vol. 22, No. 4. p 625. I996 Ekvier
Pergamon
Science
Ltd
Primed m Great Bnmin
BOOK REVIEW Stereographic
projection
techniques
I’. R. LEYSHON Published
by Butterworth
Heinemann,
in structural
geology
and R. J. LISLE l996,104p.,
fZ16.99 (ISBN o-7506-2450-7)
IBM compatible disk with two programs, one of which gives the user more practice at visualising stereograms and the other being a versatile stereogram-plotting program. This latter program is not as user-friendly as some that are available (not to be attempted without manual in hand!), but it does cover all the common procedures and can be copied and distributed as required. In general, this book is a practical and workmanlike introduction to stereograms in structural geology and will be of great use to hard-pressed lecturers with large classes and limited time, particularly those nonspecialists who find themselves teaching structural geology. It is a must for all teaching libraries, preferably in multiple copies, though students would probably prefer to buy a more general structural text, if this book were available for reference. What of those outside academia - would I recommend this book to you? Certainly - if as professional geologists you feel the need for a refresher course, if stereographic analysis of your data would be useful, but you haven’t tried it since undergraduate days, or if you find yourself plotting up data and then saying ‘So what?‘. On the negative side, like any book designed to take the place of a practical demonstration, it has a tendency to wordiness; there is no real replacement for someone at the front of the lab showing the class how things are done. Simple procedures which require only a few seconds demonstration may take a couple of complex paragraphs to be successfully described on the page. Some of the field photos could have been clearer or better labelled, though this will only be a serious problem for anyone without the opportunity to see the structural features in the field. And one final small niggle - the method recommended and employed in the book is to rotate the underlying stereographic net while keeping the tracing overlay stationary. All very well for the lab, but I would maintain that on a wet and windy Scottish hilside, it is far easier having the net in my field notebook and rotating the tracing overlay!
This large-format paperback book is designed primarily as a lab manual for undergraduates following a course in structural geology. It provides an introduction to the theory of stereographic projection, as well as exhaustive instruction on how to treat the variety of structural data likely to be encountered in the course of field mapping. Each topic or method is given a page of with the facing page being precise description, illustrations(3D sketches, maps or photos as appropriate), with the accompanying fully annotated stereogram. The book begins with a section on the measurement and recording of geological structures, followed by an introduction to the concept of lower hemisphere spherical projections. The next section encourages the reader to ‘guesstimate’ their own stereograms by visualising the projection of structural elements onto the lower hemisphere. This is an interesting way of illustrating how a stereogram works, but it is doubtful whether it will help the student who has real problems with 3D visualisation in general. There is comprehensive coverage of how to plot lines and planes accurately, which evolves from simple examples like the plunge of a fold axis, to more complex exercises such as projecting apparent lineations onto a plane; most of these sections are accompanied by geological examples of situations where such methods might be employed. There is a particularly useful section on fold analysis, including fold orientation and classification, which illustrates how stereograms vary with differences in fold shape, symmetry, interlimb angle etc. A section on folds and cleavage follows; an illustration of a typical cleavage fan would have made the discussion of bedding/cleavage asymmetry somewhat clearer. A later section tackles superposed folding and the concept of subareas or structural domains. The importance of cones and small circles is described, with examples including restoration of the tilt of beds, palaeocurrent analysis and borehole problems, and there is also brief treatment of different types of net, density counting, slip on faults, jointing and geotechnical problems. Exercises set within the text are supplemented by a final exercise list (with solutions) and there is also an
Department of Geology Aberdeen University
625
S. Goodman