Complex sentence: About a mile downstream, the railroad crossed the river on a plate girder bridge, and barely a half-mile below the railroad trestle, the lower bridge, originally built of lumber, was replaced by a three-arch stone bridge in 1902.
Split into simpler sentences: About a mile downstream, the railroad crossed the river on a plate girder bridge. And barely a half-mile below the railroad trestle, the lower bridge, originally built of lumber, was replaced by a three-arch stone bridge in 1902.