Is there an automatic principle that Medinan revelation may abrogate Meccan but not vice versa?

I understand there is a widely accepted concept of [Naskh](http://en.wikipedia.org/wiki/Naskh_%28tafsir%29#In_the_Canon) or 'abrogation' that may apply when interpreting the Quran. I also believe it to be true that it isn't known in all cases which of two verses was written first (unless they are in the same Sura), but I think I'm right in saying that all the revelation received by the Prophet in Medina was later than all the revelation received by the Prophet in the Meccan period (please correct me if that is wrong). In that case is there a general principle that in cases where Meccan and Medinan revelation appears to conflict, the Medinan revelation abrogates the Meccan? In other words Meccan revelation can never abrogate the later Medinan revelation?