Complex sentence: A steam-powered flour mill opened in 1857, and after a competing mill in nearby Drysdale was destroyed by fire in 1861 the development of Portarlington began to progress more rapidly.
Split into simpler sentences: A steam-powered flour mill opened in 1857, and after the destruction by fire of a competing mill in Drysdale. In 1861, development of Portarlington began to progress more rapidly.