Visual assessment of outcrop patterns
The previous three chapters dealt with using maps in a quantitative way. Methods were discussed of making precise measurements, where in commercial applications small errors could be costly. Now we return to the other approach to geological maps, that of making rapid visual assessments of the geology of an area. Central to this issue is an understanding of the outcrop patterns which appear on maps. Strictly, it is the junctions of outcrops, the trace showing where adjacent units meet, that we look at. The idea was introduced in chapter 2, and even at that stage we deduced from the maps the presence of features such as variably dipping beds, folds, unconformities, and faults. However, we have assumed so far that the land surface is fairly level. This is reasonable on the small-scale maps we worked with in chapter 2, but on large-scale maps the relief can become significant. This can greatly complicate the outcrop patterns and produce misleading effects. On the other hand, much can be deduced by looking at how the map units interact with the land surface. Here, we develop some general points to aid the visual appraisal of outcrop patterns on large-scale maps. We start by looking at horizontal beds, and then the effects produced by successively steeper beds.
KeywordsLand Slope Grand Canyon Canyon Wall Topographic Contour Structure Contour
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