Hi all. I'm in a bit of a fix and would be grateful if someone could help. I was going to attach an image but there's no facility for that, so if you could go on this link (genuine!!) http://webhelp.esri.com/arcgisdesktop/9.2/pdf/3D_Analyst_Tutorial.pdf Then scroll to page 44 (image on lower right corner of page) Now I have created the 3D terrain model from my DTM, I now want to create the grey bit below the green surface (making it look like its sitting on stone) can anyone help? Hope this clear enough! I’m using ArcGIS 9.1 Cheers