Three web sites that have been suggested are well worth browsing.  Bernie Gunn has assembled a monumental database of the geochemistry of volcanic rocks at http://www.geokem.com .  That, in itself,  is a magnificent resource for anyone working on the topic, but the site also has a comprehensive guide to good laboratory practice that will be invaluable to anyone beginning to work in the field., plus a host of good reference material and links.  Its quality is hardly surprising since Bernie has been engaged in geochemical research for more than 3 decades at the University of Montreal.  Another dimension to geological web resources is revealed by that compiled by Fettes College in Edinburgh at http://www.fettes.com/shetland .  It is an encyclopaedic source of environmental information on one of Britain’s many microcosms of Earth science.  It ranges from the Shetland Isles’ long geological evolution to its present geomorphology.  Fettes is a private school, with a glittering roll of alumni.  Equally encyclopaedic is http://paleodb.org , which is as near to a global database of palaeontology as you can get at present.  One of the highlights is being able to plot occurrences at the genus and species level on interactive maps, as well as browse and analyse the contents statistically.  Users do need to know how to spell taxonomic names!  Once you have compiled a map (the only trilobite whose name I can spell is Dalmanites!), you can zoom in.  If you click on an occurrence up comes a summary of the locality, with links to other parts of the database, including other fossils at the locality.  Wisely, location detail is crude enough to deter collectors from ravaging sites.  The database is compiled by 140 contributors in 11 countries.  This a site for specialists, but a beginner can learn a great deal from it.