Biology Reference
In-Depth Information
Box 5.1.
The nature of rocks
Rocks can be classified into three groups according to their origin.
1.
Igneous rocks
form between 50 and 200 kilometres below the Earth's surface
from molten rock (magma). Two types of magma are recognised: (a) basaltic
magmas which flow over the landscape as lava; and (b) silicic magmas which are
more viscous and cool below the Earth's surface to form granite-based rocks.
2.
Sedimentary rocks
form at the Earth's surface and originate from particles of
eroded rock which are deposited on ocean floors or river beds. There are two
broad types of sedimentary rocks: (a) rocks made of aggregates or fine mineral
fragments; and (b) rocks derived from chemical precipitation of organic material
such as limestone and chalk.
3.
Metamorphic rocks
are derived from igneous, sedimentary and other metamor-
phic rocks that are subjected to extreme temperature or pressure. There are many
different kinds of metamorphic rock including quartzite, schist, gneiss and marble.
Over time, softer parts of the landscape erode leaving behind hard rocky outcrops.
Water and wind continue to erode these rocks to form features that diverse and
highly specialised plants and animals have evolved to depend on.
hectares. They can be formed by granite, basalt, schist and other rock types (see
Box 5.1). Whatever type of rock they are made of, rocky outcrops share one feature
in common; that is, they have an island-like appearance because they protrude
from the surrounding landscape (Figure 5.1).
National parks and nature reserves in south-eastern Australia contain massive
sedimentary and metamorphic rock formations. Examples include places
renowned for plant species richness like the Grampians National Park (now called
Gariwerd), as well as The Rock Nature Reserve, Cocoparra National Park and the
conglomerate range of Benambra National Park (Figure 5.2).
Most of this chapter explores issues associated with small-sized (4-10 hectares)
granite outcrops; however, areas of scattered surface rock and intrusions as small
as a few isolated boulders are also important habitats on a farm. We have discussed
this type of habitat in Chapter 2, 'What makes a good remnant?'.
Rocky outcrops are extremely important for wildlife on farms and they support
a diverse range of species, particularly reptiles including skinks, geckos and large
pythons.
1, 2
Granite outcrops are a common geological feature in south-eastern
Australia but until recently their conservation values were poorly understood and
they were rarely a priority for management. In this chapter, we discuss the
common types of granite outcrops in rural landscapes and their ecological and
conservation value. We conclude the chapter by identifying threatening processes
and practical management actions that can be implemented to maintain outcrops.
