I came across a wonderful web site. The main index is here:
There are some fine dialect maps, as well as an overview of Lithuanian
dialects here:
Samogitian is the present dialect, and apparently, a formerly
full-fledged language spoken in western Lithuania. The 2nd web citation
suggests that the Samogitian dialect represents a convergent dialect, having
derived from Curonian, a now-extinct Baltic language.
'Curonia' is a new one for me, one of those 'quaint' European place/ethnic
names which just about never show up in English texts.
I don't think my 'natural' English pronunciation
of Samogitia would be correct. I see the Lithuanian version (the
adjective?) is Zemaiciai (carons over Z and C).
The terms 'Low' and 'High' Lithuanian are also new to me.