Twenty years have passed since publication of U.S. Geological Survey Professional Papers 366, Ash-flow tuffs: Their origin, geologic relations and identification, by. С S. Ross and R. L. Smith (1961), and 354-F, Zones and zonal variations in ash-flows, by R. L. Smith (I960). As these papers are now being republished, perhaps a few words are appropriate to clarify their historical evolution and to view them in the context of the present time.

Multivariate statistical methods have become commonplace in the Earth Sciences. What was once an exclusive area of activity is now within the reach of Everyman, owing to the ubiquitousness of mini-computers and the ready availability of software for doing the computing. In the days when one was required to do one's own programming, it was necessary to acquire considerable proficiency in linear algebra and one or more programming languages. Today, the vast majority of the people who use multivariate methods to analyse geological data have little or no idea of the matrix operations underlying a particular method, nor, for that matter, what the program is actually supposed to be doing. This situation can be both good and bad. It can do no harm if everything goes according to schedule, the program being used is competently constructed, which, alas, is far from being the general case, and there are no strong deviations from standard statistical theory in the data under examination. It is bad if the data do not fit the theoretical requirements of a particular method and even worse if the method of computation used is inappropriate. It is an inescapable and sad fact of life that much geological and biological material deviates in some manner or other from the theoretical requirements of a multivariate statistical procedure. The immediate relevance of this observation is that there are many sources of error in doing an analysis of geological data by means of standard statistical software.

The principal results of project 440 “Assembly and Breakup of Rodinia” of the International Geological Correlation Programme (IGCP) are reviewed in this work. A map of that supercontinent compiled using geological and paleomagnetic data describes global paleogeography 900 Ma ago. The assembly of Rodinia, which comprised most of Precambrian continental blocks, lasted ca. 400 m.y. (from 1300 to 900 Ma). Its breakup presumably triggered by mantle superplume took place between 830 and 650 Ma. The correlation between tectonic events in different continental blocks is considered. Some problems concerning the Rodinia reconstruction and history, e.g., the slow growth of juvenile crust and effects of mantle-plume events during the amalgamation period and of glaciations at the breakup time, are discussed. The latter caused changes in the biosphere and climate, whereas postglacial periods stimulated progress in biota evolution

The field of assessing the accuracy of maps derived from remotely sensed data has continued to develop and mature since the first edition of this book was published in 1999. The original eight chapters have been expanded to eleven. Of most significance is a new chapter that covers positional accuracy.