Geology Reference
In-Depth Information
Figure 3.7.
On Haytor, eastern Dartmoor, southwestern England, the Giant Granite forms most of the hill,
but Blue Granite is exposed near the base of the slope. It is evidently more susceptible to weath-
ering than the overlying rock for a shallow alcove has been formed.
Figure 3.8.
Contrasted textures of topography due to different fracture densities in granitic rock, Fafião
Valley, southern Galicia.
frequently find expression in the landscape (Fig. 3.8). Massive compartments of rock, lacking, or
with few open, fractures, withstand weathering much more readily than those riddled with open
partings. Thus, in the foothills of the western Sierra Nevada, near Fresno, in California (Larsen,
1948), there are hills underlain by norite, which on account of its mineralogy ought readily to be
weathered, but fracture density is low, water cannot penetrate the rock mass and it remains
upstanding. Similarly, basalt ought to be altered rapidly and intensely on contact with water. The
extensive and widely distributed basalt plateaux, which are prominent in many parts of the world,
