In order to get a perfect gradation between two forms in the upper and lower parts of the same formation, the deposit must have gone on continuously accumulating during a long period, sufficient for the slow process of modification;
Formazio beraren goi eta behealdeko bi formaren artean mailaketa hobezina lortzeko, metaketak etengabe pilatuz joan behar izan du astiroko eraldatze prozesuak behar bezain luzaro;