Many thanks to Kevin Wooley of Geomantics (http://www.geomantics.com/) for his image of Ayer's Rock and to Ordnance Survey ( http://www.ordsvy.gov.uk/) for their Ben Nevis map drape.
An example of overlay of geologic information may be found at:
http://www.geologie.uni-freiburg.de/projekte/grass/grass_sgi_bsp.html