Along the whole west coast, which is inhabited by a peculiar marine fauna, tertiary beds are so poorly developed that no record of several successive and peculiar marine faunas will probably be preserved to a distant age.
Itsas fauna berezia duen mendebaleko kostalde guztian zehar tertziarioko geruzak hain eskas garaturik daude, non ziurrenik han ez den aldi urrunetara arte kontserbatuko hurrenez hurreneko itsas fauna ezberdinen lekukotasunik.