Chmodding a whole directory tree

[Thought]

How do I make a whole directory tree and it's files readable by everyone?
I can't just chmod -R a+r dir because then they won't be able to cd to the
directories, but I can't chmod -R a+rx dir because then all the files will
be executable...  Is there a way to make the directories +x without making
all the files +x?  Or better yet is there a way to copy the owner's
permissions to the group and other's permissions?  Thanks