New BGS Geology Viewer 

The geological survey has released a NEW VERSION OF ITS GEOLOGY VIEWER. There is an introduction to it HERE

It seems pretty good. The screen grabs below show how it looks. There is a legend at the left side but is not very useful. To find the rock type you are best to click on the map and the rock name, age and very short description pops up. Click on "More Information" and the BGS Lexicon appears giving you all you could possibly want to know - probably.