but when tuor had lived thus in solitude as an outlaw for four years , ulmo set it in his heart to depart from the land of his fathers , for he had chosen tuor as the instrument of his designs ; and leaving once more the caves of androth he went westwards across dor-lomin , and found annon-in-gelydh , the gate of the noldor , which the people of turgon built when they dwelt in nevrast long years before .