I may add, that the only ancient tertiary formation on the west coast of South America, which has been bulky enough to resist such degradation as it has as yet suffered, but which will hardly last to a distant geological age, was deposited during a downward oscillation of level, and thus gained considerable thickness.
Erants dezaket Hego Amerikako mendebaleko kostan egundaino jasan duen erosioari eusteko bezain handia izan den, baina aro geoloiko urrun bateraino nekez iraunen duen tertziarioko antzinako formazio bakarra sestra-beherakaldi batean metatu zela, eta era horretan lodiera nahikoa hartu zuela.