Complex sentence: Trains coming from South London would run into a terminus at Holborn Viaduct (Holborn Viaduct Station) whilst trains serving local North London stations terminated at St Pancras station.
Split into simpler sentences: Trains coming from South London would run into a terminus at Holborn Viaduct (Holborn Viaduct Station). With trains serving local North London stations terminating at St Pancras station.