Complex sentence: The agreement set out the border as being a line determined by the 129th meridian east longitude, but also defined the boundary by lines running north and south from independently fixed points at Deakin and Argyle.
Split into simpler sentences: The agreement set out the border as being a line determined by the 129th meridian east longitude. However, the agreement required that the boundary be defined by lines running north and south from independently fixed points at Deakin and Argyle.