Before describing the Ammonitidae of the Lias I purpose giving a short account of the several zones of life into which this great formation is divided, with the view of defining their statigraphical distribution in time and space. More ample details on the subject will be found in the various works cited in the synonyms prefixed to the description of the different zones.

This book would not have been as it is without the trenchant editing of Heather Godwin, nor without the punctilious attentions of Stuart Proffitt. I owe them both a great debt. I sincerely thank Robin Cocks and Neale Monks for acting as scientific readers, and for commenting on sundry facts. Claire Mellish kindly drew two of the diagrams. I particularly thank Chris Stringer, Theya Molleson and Robert Kruszynski for anthropological advice. Many friends and colleagues helped me by providing illustrations and advice (they carry no responsibility if I did not heed the latter).

Epithermal Au and Ag deposits of both vein and bulk-tonnage styles may be broadly grouped into high-sulfidation (HS), intermediate-sulfidation (IS), and low-sulfidation (LS) types based on the sulfidation states of their hypogene sulfide assemblages. The HS and LS types may be subdivided using additional parameters, particularly related igneous rock types and metal content.

This paper describes a methodology of translating mineral deposit models into flexible probabilistic structures based on (1) extraction of ore components (fluids, metals, and ligands) from crustal or mantle sources or both, (2) fluid- or melt-assisted transport of ore components from source to trap zones, (3) formation of trap zones (i.e., effective melt or fluid channels) that can focus melt or fluid migration and accommodate large amounts of metal, and (4) operation of the physicochemical processes that promote and sustain the deposition of metal from fluids or melts passing through a particular trap site.