Browns Field

The Fox Valley diatreme is about 300 metres in diameter with extensions or annexes on its eastern and western sides. The diatreme centre has been developed as a sports oval and rock exposure is limited to the creek bed and banks on its eastern side. The rocks are mostly weathered and inclined to fragment, but a contact zone with Hawkesbury Sandstone is well exposed just inside the main track entrance. The contact shows the strong shearing that is typically caused by downward slumping of the main mass of the diatreme.

The scattered creek bed outcrops are of layered sedimentary rocks and volcanic tuffs and breccias which carry pieces of basalt and fragments and blocks of sedimentary rocks such as sandstone, shale and even coal. Many samples were collected for microscope thin section examination, and typically these show no or very little effect of magmatic heat. These included both shattered fragments torn from the wallrocks and probably also from a layered succession in the diatreme.

Vegetation

The natural vegetation appears to be mainly warm temperate rainforest which is preserved to the east of the oval. Trees include coachwood, sassafras, lillypilly, sandpaper fig and cabbage tree palm. Subtropical elements are also present, including trial plantings in the eastern annex within the Cooper Crescent loop. Trees here include giant stinging tree, blue quandong, pencil cedar, white belly gum and featherwood. There are many species of large and small shrubs, including bolwarra and native hydrangea not to mention climbers like water vine (Cissus) species, morinda, pearl vine and wombat berry.