[xsl] Need to get lowest and highest date values

["watchstone@xxxxxxxxxxx" <watchstone@xxxxxxxxxxx>]

I have a series of dates in my source document in the form:

1850-1920
1900-1940
1924-1960
1950-1974

I want to get the minimum and maximum values and output them in the same format.  In this case:

1850-1974

What is the best way to do this?  A 1.0 solution would be appreciated.  Thanks.