In 1858, the State of Alabama, seeking to develop coal and iron industries in Jefferson County, had John T. Milner survey Shades Mountain for the most practical route for the South and North Railroad to cross, and he selected Brock's Gap, named for original land purchaser Pinkney L. Brock. Work began immediately, and the cut now passing under South Shades Crest Road was blasted by nitroglycerin through a bed of limestone 75 feet deep and was hailed as the deepest railroad cut in the world. Delayed by the Civil War, work on the line was finally completed in 1871 by the firm of Bartley and Boyles of Helena under Supt. J.F.B. Jackson. Birmingham, Alabama's first industrial city, developed around the intersection of the South and North Railroad with the Alabama and Chattanooga Railroad as an important transportation center, and after the ravages of the Civil War it became a city of the New South as many destitute men rushed there to find work in the mines or on the railroads. The South and North Railroad later became part of the L & N Railroad system, and when L & N built the tunnel now in use under South Shades Crest Road, the old route became obsolete; the old railroad bed remains visible on the opposite side of the road, and the ground around the cut is littered with large blocks of stone cut from the mountain.