Reading ''Journeys,'' one senses civilization everywhere going through something like a midlife crisis. Yet Miss Morris is no doom- presager; she doesn't preach to us about anomie, or the claustrophobia arising out of a homogenization of cultures. She writes as if the true monuments of our time were our mistakes, as classical, immense and moving as any cathedral. Other ages aimed at permanence and immortality, but the peculiar genius of ours may lie in transience and mortality