Question: how to number sections as (a,b,c) rather than (1,2,3)

Hello:

I would like to have my section numbering as follows:

1. Section One
     1a) this is section 1.1
     1b) this is section 1.2
2. Section 2
    2a) this is section 2.1

Has anyone on the list done something like this?

Thanks in advance!

--Craeg