Movement of the Earth’s Surface from Within - Southern England - page 37

FIG 33. The most important types of folds and faults, and the local patterns of forces re-
sponsible.
Vertical changes by erosion or deposition
Addition or subtraction of material to the surface of the Earth is happening all the time
as sediment is deposited or solid material is eroded. The field of sedimentology is con-
cerned with the wide range of different processes that are involved in the erosion, trans-
port and deposition of material, whether the primary agent of movement is water, ice,
mud or wind. An important point is that few of these sedimentary processes relate dir-
ectly to the large tectonic movements of the Earth's crust that we have discussed above.
Scenery is often produced by erosion of thick deposits that formed in sedimentary
basins where material eroded from the surrounding uplands accumulated. One of the
characteristic features of these thick deposits is their layered appearance, which is of-
ten visible in the scenery. Layering varies from millimetre-scale laminations produced
by very small fluctuations in depositional processes, to sheets hundreds of metres thick
that extend across an entire sedimentary basin. These thicker sheets are often so dis-
tinctive that they are named and mapped as separate geological units representing sig-
nificant changes in the local environment at the time they were deposited.