|Mount Lindesay from the south|
Mount Lindesay gets its shape by the rhyolite that forms the top most layer. The rhyolite is hard, resistant to weathering and therefore remains relatively difficult to erode. It is for this reason that the rhyolite has protected the underlying softer rock at Mount Lindsay and you can see the same process for ridges to the east and south of the mountain too. The actual vents for the rhyolite and underlying basalt lavas is actually a little tricky to definitely locate but we do know that the main volcanic centre for these rocks was at the Focal Peak Volcano located in the vicinity of present day Mount Barney a significant distance to the north. Additionally, there are some real volcanic plugs further to the west which I mention below.
Rhyolite from focal peak was thought by Duggan and Mason (1978) and other authors to extend as far Nimbin to the east. However, recent work by Cotter (1998) has shown that this is not the case but the Binna Burra Rhyolite still extends a long way to the east past places like Wiangaree.
There are however, some clearly identifiable volcanic plugs in the region. A good one is sometimes referred to as the Nightcap Peak and is located half way between Woodenbong and Urbenville just a little to the west of the road. It stands out from the rolling hills, is difficult to miss and is made from the rock granophyre (fine grained granite-like rock). At Urbenville the Northern Obelisk is another example of a plug, a bit one! Additionally, large dykes exist to the south west of Urbenville too.
*Cotter, S. 1998. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of North Eastern New South Wales. Masters Thesis, Southern Cross University.
*Duggan, P.B., Mason, D.R. 1978. Stratigraphy of the Lamington Volcanics in Far Northeastern New South Wales. Australian Journal of Earth Sciences V25.