"Declivous" is a word in ENGLISH

Everything that falls upon the eye is an apparition, a sheet dropped over the world's true workings. The nerves & brain are tricked, and one is left with dreams that these specters loose their hands from ours and walk away...so familiar as to imply that they should be permanent fixtures of the world, when in fact nothing is more perishable...Why must we be left, the survivors picking among flotsam, among the small, unnoticed, unvalued clutter that remained when they vanished, that only catastrophe had made notable?...It seemed to me that what perished need not also be lost.