Dewsbury.
_Cash_ is from the French _caisse_, the moneychest where _specie_ was kept.
So _caissier_ became "cashier," and _specie_ "cash."
_Mob_, Swift tells us (_Polite Conversation_, Introd.), is a contraction
for _mobile_.
CLERICUS RUSTICUS has not, I fear, Johnson's _Dictionary_, where both these
derivations are given.