[Tagging] Specific natural-tags for rock and stone.

[Johan Jönsson]

In the discussion of natural=bare_rock I have found that there is need for 
a couple of different specific natural-tags for stone and rock land forms.
for instance the boulder fields and other areas of lose rock that are not scree.

It would be nice if we could find a hierachical tagging system in the same way as
natural=wetland + wetland=bog  
see http://wiki.openstreetmap.org/wiki/Wetland

and in
natural=desert + desert=hammada  
see http://wiki.openstreetmap.org/wiki/Proposed_features/Deserts

/Johan Jönsson