Geology Reference
In-Depth Information
(a)
(b)
Figure 5.3.
(a) Well-rounded boulder, Devil's Marbles, NorthernTerritory. (b) Slightly less well-rounded
boulder, Herbert River Falls area, north Queensland.
between the still solid rounded mass and the weathered material or regolith is the weathering front.
In this instance, it is roughly spherical or ellipsoidal in shape rather than essentially planate, but it
is nevertheless the limit of weathering and hence is the weathering front.
In most instances, the corestones are of the same composition as were the rest of the host
blocks; they are not inherently more resistant than the marginal areas. That the complex of core-
stones and grus is
in situ
is demonstrated by the presence of veins traversing the entire rock mass
(Fig. 5.5).
Corestones of intrinsically fresh granite set in a matrix of weathered, friable rock are
examples of spheroidal weathering (Ollier, 1971). They also represent the first stage in the devel-
opment of boulders.
