The age of formation of the Lapstone Monocline has been long considered to be late Pliocene/early Pleistocene (the Kosciusko Uplift) but it is now generally thought to be much older. Palaeomagnetic data from haematite‐rich beds within the Hawkesbury Sandstone on and about the monocline indicate that it formed before the oldest haematite was introduced to these beds. The age of this oldest haematite is 15±7 Ma. On the basis of these data, the age of the monocline is unlikely to be less than 8 Ma, probably exceeds 15 Ma, and could be older than 22 Ma.