now there are none such delvers of earth or rock as the noldoli ( and this melko knows ) , but in those places is the earth of a great hardness ; and tuor said : `` the rocks of the hill of amon gwareth are as iron , and only with much travail may they be cloven ; yet if this be done in secret then must great time and patience be added ; but the stone of the floor of the vale of tumladin is as forged steel , nor may it be hewn without the knowledge of the gondothlim save in moons and years . ''