Before posting to any newsgroup it is good "netiquette" to familiarise yourself with the Frequently Asked Questions on that group. Answers to FAQs for sci.geo.geology are maintained by Spencer Ramshaw and Phillip Ingram.
They are visible here and are also archived at rtfm.mit.edu; clicking on the following will give ftp access to the various sections ftp://rtfm.mit.edu/pub/usenet-by-group/news.answers/geology-faq/.