Combine the quantitative backgrounds of geophysics with the graphical traditions of geology in the presence of a wealth of measurements and you find the sorts of analyses standard in paleomagnetism. The kinds of analyses common to paleomagnetism are quite amenable to incorporation in a program with a graphical interface, such as the Macintosh. This program represents an effort to provide an environment for the interactive analysis of paleomagnetic data that is responsive, flexible, and friendly to the user.

The pedigree of this code is complex. The core of the program is a collection of routines initially written for the Apple II to take paleomagnetic directions and apply the least-squares fitting algorithm of Kirschvink (1980) to get a best-fit estimate of remanent directions for samples. Kirschvink and other programmers through the years made modifications to the code to make it somewhat easier to use and to expand some of the capabilities of the code. Other codes to plot "Zijderveld" (now properly termed "Orthographic" plots, to believe those who care) and equal area plots were developed over this time. These codes were later modified and ported to the IBM PC.

In 1989 Rob Ripperdan and I decided to convert the codes from the PC to the Mac and construct an interface more in line with the type of data analysis we desired. Rob ported the code to the Mac and checked that it ran properly as it had on the PC. I worked on the interface, providing a multiple window environment and user-directed interface. This code incorporated the least-squares fitting algorithm, equal area plots, and "Zijderveld" plots.

The last section of this manual documents the growth of the code. Work has focused on the improvement of the interface, addition of other graphical elements like stratigraphic ("strat") plots, and some improvement to the statistics (mainly the addition of "Non-parametric statistics"). There has not been such a great effort in adding statistics (bootstraps, fold tests, reversal tests, averaging of secular variation, VGP statistics, ΔR and ΔF values) mainly because there seems to be considerable variation in what statistics are desired by different workers. With the addition of a Means file in v2.0 of this code, it is now straightforward to take statistical means from this code and plug them into other programs to do whatever statistical tests the user desires.

So the logic of the present code is that measurements made on a magnetometer can be imported into this program. Data can be quickly examined to see what patterns might be present, then the measurements can be considered in greater detail and the results of constructing least-squares fits can then be analyzed and compared between samples, sites and localities. The idea is to make analysis simple and intuitive and to provide enough different ways of viewing the data so that the simple hypotheses of common paleomagetic analysis can be quickly checked. The final object is to provide the best possible analysis of paleomagnetic data free of the bias sometimes introduced by the "it's too hard to look at the data again" factor.

This code is not a commercial product; it was developed by scientists working in paleomagnetic studies and so it lacks the testing and finesse that you might expect of a commercial product. We do not have a staff testing the program under lots of different conditions; thus the only way for us to learn of errors, bugs, and design flaws is for people to complain and provide some feedback. Similarly, if you like the code and use it, let us know; if you use figures from the program in scientific publications, acknowledging the use of this code might be nice (after all, making a code like this doesn't really help get research grants or jobs; it is as much a public service as anything else). I wouldn't mind seeing reprints of papers published using this code; seeing the modifications made to figures derived from this code might suggest future improvements (and provide motivation).

Although distributed freely, the source code is copyrighted by C. H. Jones and the California Institute of Technology and cannot be distributed commercially for profit without first contacting me.

Craig Jones
Cooperative Institute for Research in Environmental Science (CIRES)
Campus Box 216
University of Colorado at Boulder
Boulder, CO

Return to PaleoMag overview

Table of Contents

Next section