SINGULAR ACCIDENT AT WHITEHAVEN. - A somewhat singular, though serious, accident occurred in Whitehaven on Sunday, about noon, to MR. SAMUEL STEWART, clothier and outfitter, Market-place, Whitehaven.  MR. STEWART, who is an elderly man, was passing along Low King-street, and when near to the Globe Hotel, a large dog which was running along the street came in contact with him, with the result that MR. STEWART was knocked down, his head coming in violent contact with the ground, and he was rendered insensible.  He was taken home in a cab, and DR. MUIR was called in, and MR. STEWART was brought around.  His ankle was found to be sprained, and the shock to the system was exceedingly severe.