about three o'clock
I had never thought of it before , but I now resolved to be upon my guard . Indeed , I thought that this halt would mark the termination of our walk ; but I was mistaken , for , instead of returning to the Nautilus , Captain Nemo continued his bold excursion . The ground was still on the incline , its declivity seemed to be getting greater , and to be leading us to greater depths . It must have been about three o'clock when we reached a narrow valley , between high perpendicular walls , situated about seventy-five fathoms deep . Thanks to the perfection of our apparatus , we were forty-five fathoms below the limit which nature seems to have imposed on man as to his submarine excursions . I say seventy-five fathoms , though I had no instrument by which to judge the distance . But I knew that even in the clearest waters the solar rays could not penetrate further .