I'll leave PriaposLovs to tackle your friend's first name of "Thessalie", as that sounds suspiciously like a placename in Greece to me.
"Gaskarth" is an English surname meaning "goose garth" (enclosure). As stated at this website:
http://www.dimensional.com/~gizmo42/threlk.html
"...presumably denoting the situation of the cottage where the man lived who was first given this name..."
-- Nanaea